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+# postgresql/base.py
+# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+
+r"""
+.. dialect:: postgresql
+    :name: PostgreSQL
+    :full_support: 9.6, 10, 11, 12, 13, 14
+    :normal_support: 9.6+
+    :best_effort: 8+
+
+.. _postgresql_sequences:
+
+Sequences/SERIAL/IDENTITY
+-------------------------
+
+PostgreSQL supports sequences, and SQLAlchemy uses these as the default means
+of creating new primary key values for integer-based primary key columns. When
+creating tables, SQLAlchemy will issue the ``SERIAL`` datatype for
+integer-based primary key columns, which generates a sequence and server side
+default corresponding to the column.
+
+To specify a specific named sequence to be used for primary key generation,
+use the :func:`~sqlalchemy.schema.Sequence` construct::
+
+    Table('sometable', metadata,
+            Column('id', Integer, Sequence('some_id_seq'), primary_key=True)
+        )
+
+When SQLAlchemy issues a single INSERT statement, to fulfill the contract of
+having the "last insert identifier" available, a RETURNING clause is added to
+the INSERT statement which specifies the primary key columns should be
+returned after the statement completes. The RETURNING functionality only takes
+place if PostgreSQL 8.2 or later is in use. As a fallback approach, the
+sequence, whether specified explicitly or implicitly via ``SERIAL``, is
+executed independently beforehand, the returned value to be used in the
+subsequent insert. Note that when an
+:func:`~sqlalchemy.sql.expression.insert()` construct is executed using
+"executemany" semantics, the "last inserted identifier" functionality does not
+apply; no RETURNING clause is emitted nor is the sequence pre-executed in this
+case.
+
+To force the usage of RETURNING by default off, specify the flag
+``implicit_returning=False`` to :func:`_sa.create_engine`.
+
+PostgreSQL 10 and above IDENTITY columns
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+PostgreSQL 10 and above have a new IDENTITY feature that supersedes the use
+of SERIAL. The :class:`_schema.Identity` construct in a
+:class:`_schema.Column` can be used to control its behavior::
+
+    from sqlalchemy import Table, Column, MetaData, Integer, Computed
+
+    metadata = MetaData()
+
+    data = Table(
+        "data",
+        metadata,
+        Column(
+            'id', Integer, Identity(start=42, cycle=True), primary_key=True
+        ),
+        Column('data', String)
+    )
+
+The CREATE TABLE for the above :class:`_schema.Table` object would be:
+
+.. sourcecode:: sql
+
+    CREATE TABLE data (
+        id INTEGER GENERATED BY DEFAULT AS IDENTITY (START WITH 42 CYCLE),
+        data VARCHAR,
+        PRIMARY KEY (id)
+    )
+
+.. versionchanged::  1.4   Added :class:`_schema.Identity` construct
+   in a :class:`_schema.Column` to specify the option of an autoincrementing
+   column.
+
+.. note::
+
+   Previous versions of SQLAlchemy did not have built-in support for rendering
+   of IDENTITY, and could use the following compilation hook to replace
+   occurrences of SERIAL with IDENTITY::
+
+       from sqlalchemy.schema import CreateColumn
+       from sqlalchemy.ext.compiler import compiles
+
+
+       @compiles(CreateColumn, 'postgresql')
+       def use_identity(element, compiler, **kw):
+           text = compiler.visit_create_column(element, **kw)
+           text = text.replace(
+               "SERIAL", "INT GENERATED BY DEFAULT AS IDENTITY"
+            )
+           return text
+
+   Using the above, a table such as::
+
+       t = Table(
+           't', m,
+           Column('id', Integer, primary_key=True),
+           Column('data', String)
+       )
+
+   Will generate on the backing database as::
+
+       CREATE TABLE t (
+           id INT GENERATED BY DEFAULT AS IDENTITY,
+           data VARCHAR,
+           PRIMARY KEY (id)
+       )
+
+.. _postgresql_ss_cursors:
+
+Server Side Cursors
+-------------------
+
+Server-side cursor support is available for the psycopg2, asyncpg
+dialects and may also be available in others.
+
+Server side cursors are enabled on a per-statement basis by using the
+:paramref:`.Connection.execution_options.stream_results` connection execution
+option::
+
+    with engine.connect() as conn:
+        result = conn.execution_options(stream_results=True).execute(text("select * from table"))
+
+Note that some kinds of SQL statements may not be supported with
+server side cursors; generally, only SQL statements that return rows should be
+used with this option.
+
+.. deprecated:: 1.4  The dialect-level server_side_cursors flag is deprecated
+   and will be removed in a future release.  Please use the
+   :paramref:`_engine.Connection.stream_results` execution option for
+   unbuffered cursor support.
+
+.. seealso::
+
+    :ref:`engine_stream_results`
+
+.. _postgresql_isolation_level:
+
+Transaction Isolation Level
+---------------------------
+
+Most SQLAlchemy dialects support setting of transaction isolation level
+using the :paramref:`_sa.create_engine.isolation_level` parameter
+at the :func:`_sa.create_engine` level, and at the :class:`_engine.Connection`
+level via the :paramref:`.Connection.execution_options.isolation_level`
+parameter.
+
+For PostgreSQL dialects, this feature works either by making use of the
+DBAPI-specific features, such as psycopg2's isolation level flags which will
+embed the isolation level setting inline with the ``"BEGIN"`` statement, or for
+DBAPIs with no direct support by emitting ``SET SESSION CHARACTERISTICS AS
+TRANSACTION ISOLATION LEVEL <level>`` ahead of the ``"BEGIN"`` statement
+emitted by the DBAPI.   For the special AUTOCOMMIT isolation level,
+DBAPI-specific techniques are used which is typically an ``.autocommit``
+flag on the DBAPI connection object.
+
+To set isolation level using :func:`_sa.create_engine`::
+
+    engine = create_engine(
+        "postgresql+pg8000://scott:tiger@localhost/test",
+        isolation_level = "REPEATABLE READ"
+    )
+
+To set using per-connection execution options::
+
+    with engine.connect() as conn:
+        conn = conn.execution_options(
+            isolation_level="REPEATABLE READ"
+        )
+        with conn.begin():
+            # ... work with transaction
+
+There are also more options for isolation level configurations, such as
+"sub-engine" objects linked to a main :class:`_engine.Engine` which each apply
+different isolation level settings.  See the discussion at
+:ref:`dbapi_autocommit` for background.
+
+Valid values for ``isolation_level`` on most PostgreSQL dialects include:
+
+* ``READ COMMITTED``
+* ``READ UNCOMMITTED``
+* ``REPEATABLE READ``
+* ``SERIALIZABLE``
+* ``AUTOCOMMIT``
+
+.. seealso::
+
+    :ref:`dbapi_autocommit`
+
+    :ref:`postgresql_readonly_deferrable`
+
+    :ref:`psycopg2_isolation_level`
+
+    :ref:`pg8000_isolation_level`
+
+.. _postgresql_readonly_deferrable:
+
+Setting READ ONLY / DEFERRABLE
+------------------------------
+
+Most PostgreSQL dialects support setting the "READ ONLY" and "DEFERRABLE"
+characteristics of the transaction, which is in addition to the isolation level
+setting. These two attributes can be established either in conjunction with or
+independently of the isolation level by passing the ``postgresql_readonly`` and
+``postgresql_deferrable`` flags with
+:meth:`_engine.Connection.execution_options`.  The example below illustrates
+passing the ``"SERIALIZABLE"`` isolation level at the same time as setting
+"READ ONLY" and "DEFERRABLE"::
+
+    with engine.connect() as conn:
+        conn = conn.execution_options(
+            isolation_level="SERIALIZABLE",
+            postgresql_readonly=True,
+            postgresql_deferrable=True
+        )
+        with conn.begin():
+            #  ... work with transaction
+
+Note that some DBAPIs such as asyncpg only support "readonly" with
+SERIALIZABLE isolation.
+
+.. versionadded:: 1.4 added support for the ``postgresql_readonly``
+   and ``postgresql_deferrable`` execution options.
+
+.. _postgresql_alternate_search_path:
+
+Setting Alternate Search Paths on Connect
+------------------------------------------
+
+The PostgreSQL ``search_path`` variable refers to the list of schema names
+that will be implicitly referred towards when a particular table or other
+object is referenced in a SQL statement.  As detailed in the next section
+:ref:`postgresql_schema_reflection`, SQLAlchemy is generally organized around
+the concept of keeping this variable at its default value of ``public``,
+however, in order to have it set to any arbitrary name or names when connections
+are used automatically, the "SET SESSION search_path" command may be invoked
+for all connections in a pool using the following event handler, as discussed
+at :ref:`schema_set_default_connections`::
+
+    from sqlalchemy import event
+    from sqlalchemy import create_engine
+
+    engine = create_engine("postgresql+psycopg2://scott:tiger@host/dbname")
+
+    @event.listens_for(engine, "connect", insert=True)
+    def set_search_path(dbapi_connection, connection_record):
+        existing_autocommit = dbapi_connection.autocommit
+        dbapi_connection.autocommit = True
+        cursor = dbapi_connection.cursor()
+        cursor.execute("SET SESSION search_path='%s'" % schema_name)
+        cursor.close()
+        dbapi_connection.autocommit = existing_autocommit
+
+The reason the recipe is complicated by use of the ``.autocommit`` DBAPI
+attribute is so that when the ``SET SESSION search_path`` directive is invoked,
+it is invoked outside of the scope of any transaction and therefore will not
+be reverted when the DBAPI connection has a rollback.
+
+.. seealso::
+
+  :ref:`schema_set_default_connections` - in the :ref:`metadata_toplevel` documentation
+
+
+
+
+.. _postgresql_schema_reflection:
+
+Remote-Schema Table Introspection and PostgreSQL search_path
+------------------------------------------------------------
+
+.. admonition:: Section Best Practices Summarized
+
+    keep the ``search_path`` variable set to its default of ``public``, without
+    any other schema names. For other schema names, name these explicitly
+    within :class:`_schema.Table` definitions. Alternatively, the
+    ``postgresql_ignore_search_path`` option will cause all reflected
+    :class:`_schema.Table` objects to have a :attr:`_schema.Table.schema`
+    attribute set up.
+
+The PostgreSQL dialect can reflect tables from any schema, as outlined in
+:ref:`metadata_reflection_schemas`.
+
+With regards to tables which these :class:`_schema.Table`
+objects refer to via foreign key constraint, a decision must be made as to how
+the ``.schema`` is represented in those remote tables, in the case where that
+remote schema name is also a member of the current
+`PostgreSQL search path
+<https://www.postgresql.org/docs/current/static/ddl-schemas.html#DDL-SCHEMAS-PATH>`_.
+
+By default, the PostgreSQL dialect mimics the behavior encouraged by
+PostgreSQL's own ``pg_get_constraintdef()`` builtin procedure.  This function
+returns a sample definition for a particular foreign key constraint,
+omitting the referenced schema name from that definition when the name is
+also in the PostgreSQL schema search path.  The interaction below
+illustrates this behavior::
+
+    test=> CREATE TABLE test_schema.referred(id INTEGER PRIMARY KEY);
+    CREATE TABLE
+    test=> CREATE TABLE referring(
+    test(>         id INTEGER PRIMARY KEY,
+    test(>         referred_id INTEGER REFERENCES test_schema.referred(id));
+    CREATE TABLE
+    test=> SET search_path TO public, test_schema;
+    test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
+    test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
+    test-> ON n.oid = c.relnamespace
+    test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
+    test-> WHERE c.relname='referring' AND r.contype = 'f'
+    test-> ;
+                   pg_get_constraintdef
+    ---------------------------------------------------
+     FOREIGN KEY (referred_id) REFERENCES referred(id)
+    (1 row)
+
+Above, we created a table ``referred`` as a member of the remote schema
+``test_schema``, however when we added ``test_schema`` to the
+PG ``search_path`` and then asked ``pg_get_constraintdef()`` for the
+``FOREIGN KEY`` syntax, ``test_schema`` was not included in the output of
+the function.
+
+On the other hand, if we set the search path back to the typical default
+of ``public``::
+
+    test=> SET search_path TO public;
+    SET
+
+The same query against ``pg_get_constraintdef()`` now returns the fully
+schema-qualified name for us::
+
+    test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
+    test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
+    test-> ON n.oid = c.relnamespace
+    test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
+    test-> WHERE c.relname='referring' AND r.contype = 'f';
+                         pg_get_constraintdef
+    ---------------------------------------------------------------
+     FOREIGN KEY (referred_id) REFERENCES test_schema.referred(id)
+    (1 row)
+
+SQLAlchemy will by default use the return value of ``pg_get_constraintdef()``
+in order to determine the remote schema name.  That is, if our ``search_path``
+were set to include ``test_schema``, and we invoked a table
+reflection process as follows::
+
+    >>> from sqlalchemy import Table, MetaData, create_engine, text
+    >>> engine = create_engine("postgresql://scott:tiger@localhost/test")
+    >>> with engine.connect() as conn:
+    ...     conn.execute(text("SET search_path TO test_schema, public"))
+    ...     metadata_obj = MetaData()
+    ...     referring = Table('referring', metadata_obj,
+    ...                       autoload_with=conn)
+    ...
+    <sqlalchemy.engine.result.CursorResult object at 0x101612ed0>
+
+The above process would deliver to the :attr:`_schema.MetaData.tables`
+collection
+``referred`` table named **without** the schema::
+
+    >>> metadata_obj.tables['referred'].schema is None
+    True
+
+To alter the behavior of reflection such that the referred schema is
+maintained regardless of the ``search_path`` setting, use the
+``postgresql_ignore_search_path`` option, which can be specified as a
+dialect-specific argument to both :class:`_schema.Table` as well as
+:meth:`_schema.MetaData.reflect`::
+
+    >>> with engine.connect() as conn:
+    ...     conn.execute(text("SET search_path TO test_schema, public"))
+    ...     metadata_obj = MetaData()
+    ...     referring = Table('referring', metadata_obj,
+    ...                       autoload_with=conn,
+    ...                       postgresql_ignore_search_path=True)
+    ...
+    <sqlalchemy.engine.result.CursorResult object at 0x1016126d0>
+
+We will now have ``test_schema.referred`` stored as schema-qualified::
+
+    >>> metadata_obj.tables['test_schema.referred'].schema
+    'test_schema'
+
+.. sidebar:: Best Practices for PostgreSQL Schema reflection
+
+    The description of PostgreSQL schema reflection behavior is complex, and
+    is the product of many years of dealing with widely varied use cases and
+    user preferences. But in fact, there's no need to understand any of it if
+    you just stick to the simplest use pattern: leave the ``search_path`` set
+    to its default of ``public`` only, never refer to the name ``public`` as
+    an explicit schema name otherwise, and refer to all other schema names
+    explicitly when building up a :class:`_schema.Table` object.  The options
+    described here are only for those users who can't, or prefer not to, stay
+    within these guidelines.
+
+Note that **in all cases**, the "default" schema is always reflected as
+``None``. The "default" schema on PostgreSQL is that which is returned by the
+PostgreSQL ``current_schema()`` function.  On a typical PostgreSQL
+installation, this is the name ``public``.  So a table that refers to another
+which is in the ``public`` (i.e. default) schema will always have the
+``.schema`` attribute set to ``None``.
+
+.. seealso::
+
+    :ref:`reflection_schema_qualified_interaction` - discussion of the issue
+    from a backend-agnostic perspective
+
+    `The Schema Search Path
+    <https://www.postgresql.org/docs/current/static/ddl-schemas.html#DDL-SCHEMAS-PATH>`_
+    - on the PostgreSQL website.
+
+INSERT/UPDATE...RETURNING
+-------------------------
+
+The dialect supports PG 8.2's ``INSERT..RETURNING``, ``UPDATE..RETURNING`` and
+``DELETE..RETURNING`` syntaxes.   ``INSERT..RETURNING`` is used by default
+for single-row INSERT statements in order to fetch newly generated
+primary key identifiers.   To specify an explicit ``RETURNING`` clause,
+use the :meth:`._UpdateBase.returning` method on a per-statement basis::
+
+    # INSERT..RETURNING
+    result = table.insert().returning(table.c.col1, table.c.col2).\
+        values(name='foo')
+    print(result.fetchall())
+
+    # UPDATE..RETURNING
+    result = table.update().returning(table.c.col1, table.c.col2).\
+        where(table.c.name=='foo').values(name='bar')
+    print(result.fetchall())
+
+    # DELETE..RETURNING
+    result = table.delete().returning(table.c.col1, table.c.col2).\
+        where(table.c.name=='foo')
+    print(result.fetchall())
+
+.. _postgresql_insert_on_conflict:
+
+INSERT...ON CONFLICT (Upsert)
+------------------------------
+
+Starting with version 9.5, PostgreSQL allows "upserts" (update or insert) of
+rows into a table via the ``ON CONFLICT`` clause of the ``INSERT`` statement. A
+candidate row will only be inserted if that row does not violate any unique
+constraints.  In the case of a unique constraint violation, a secondary action
+can occur which can be either "DO UPDATE", indicating that the data in the
+target row should be updated, or "DO NOTHING", which indicates to silently skip
+this row.
+
+Conflicts are determined using existing unique constraints and indexes.  These
+constraints may be identified either using their name as stated in DDL,
+or they may be inferred by stating the columns and conditions that comprise
+the indexes.
+
+SQLAlchemy provides ``ON CONFLICT`` support via the PostgreSQL-specific
+:func:`_postgresql.insert()` function, which provides
+the generative methods :meth:`_postgresql.Insert.on_conflict_do_update`
+and :meth:`~.postgresql.Insert.on_conflict_do_nothing`:
+
+.. sourcecode:: pycon+sql
+
+    >>> from sqlalchemy.dialects.postgresql import insert
+    >>> insert_stmt = insert(my_table).values(
+    ...     id='some_existing_id',
+    ...     data='inserted value')
+    >>> do_nothing_stmt = insert_stmt.on_conflict_do_nothing(
+    ...     index_elements=['id']
+    ... )
+    >>> print(do_nothing_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO NOTHING
+    {stop}
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     constraint='pk_my_table',
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT ON CONSTRAINT pk_my_table DO UPDATE SET data = %(param_1)s
+
+.. versionadded:: 1.1
+
+.. seealso::
+
+    `INSERT .. ON CONFLICT
+    <https://www.postgresql.org/docs/current/static/sql-insert.html#SQL-ON-CONFLICT>`_
+    - in the PostgreSQL documentation.
+
+Specifying the Target
+^^^^^^^^^^^^^^^^^^^^^
+
+Both methods supply the "target" of the conflict using either the
+named constraint or by column inference:
+
+* The :paramref:`_postgresql.Insert.on_conflict_do_update.index_elements` argument
+  specifies a sequence containing string column names, :class:`_schema.Column`
+  objects, and/or SQL expression elements, which would identify a unique
+  index:
+
+  .. sourcecode:: pycon+sql
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     index_elements=['id'],
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
+    {stop}
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     index_elements=[my_table.c.id],
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
+
+* When using :paramref:`_postgresql.Insert.on_conflict_do_update.index_elements` to
+  infer an index, a partial index can be inferred by also specifying the
+  use the :paramref:`_postgresql.Insert.on_conflict_do_update.index_where` parameter:
+
+  .. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(user_email='a@b.com', data='inserted data')
+    >>> stmt = stmt.on_conflict_do_update(
+    ...     index_elements=[my_table.c.user_email],
+    ...     index_where=my_table.c.user_email.like('%@gmail.com'),
+    ...     set_=dict(data=stmt.excluded.data)
+    ... )
+    >>> print(stmt)
+    {opensql}INSERT INTO my_table (data, user_email)
+    VALUES (%(data)s, %(user_email)s) ON CONFLICT (user_email)
+    WHERE user_email LIKE %(user_email_1)s DO UPDATE SET data = excluded.data
+
+* The :paramref:`_postgresql.Insert.on_conflict_do_update.constraint` argument is
+  used to specify an index directly rather than inferring it.  This can be
+  the name of a UNIQUE constraint, a PRIMARY KEY constraint, or an INDEX:
+
+  .. sourcecode:: pycon+sql
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     constraint='my_table_idx_1',
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT ON CONSTRAINT my_table_idx_1 DO UPDATE SET data = %(param_1)s
+    {stop}
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     constraint='my_table_pk',
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT ON CONSTRAINT my_table_pk DO UPDATE SET data = %(param_1)s
+    {stop}
+
+* The :paramref:`_postgresql.Insert.on_conflict_do_update.constraint` argument may
+  also refer to a SQLAlchemy construct representing a constraint,
+  e.g. :class:`.UniqueConstraint`, :class:`.PrimaryKeyConstraint`,
+  :class:`.Index`, or :class:`.ExcludeConstraint`.   In this use,
+  if the constraint has a name, it is used directly.  Otherwise, if the
+  constraint is unnamed, then inference will be used, where the expressions
+  and optional WHERE clause of the constraint will be spelled out in the
+  construct.  This use is especially convenient
+  to refer to the named or unnamed primary key of a :class:`_schema.Table`
+  using the
+  :attr:`_schema.Table.primary_key` attribute:
+
+  .. sourcecode:: pycon+sql
+
+    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
+    ...     constraint=my_table.primary_key,
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
+
+The SET Clause
+^^^^^^^^^^^^^^^
+
+``ON CONFLICT...DO UPDATE`` is used to perform an update of the already
+existing row, using any combination of new values as well as values
+from the proposed insertion.   These values are specified using the
+:paramref:`_postgresql.Insert.on_conflict_do_update.set_` parameter.  This
+parameter accepts a dictionary which consists of direct values
+for UPDATE:
+
+.. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(id='some_id', data='inserted value')
+    >>> do_update_stmt = stmt.on_conflict_do_update(
+    ...     index_elements=['id'],
+    ...     set_=dict(data='updated value')
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
+
+.. warning::
+
+    The :meth:`_expression.Insert.on_conflict_do_update`
+    method does **not** take into
+    account Python-side default UPDATE values or generation functions, e.g.
+    those specified using :paramref:`_schema.Column.onupdate`.
+    These values will not be exercised for an ON CONFLICT style of UPDATE,
+    unless they are manually specified in the
+    :paramref:`_postgresql.Insert.on_conflict_do_update.set_` dictionary.
+
+Updating using the Excluded INSERT Values
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In order to refer to the proposed insertion row, the special alias
+:attr:`~.postgresql.Insert.excluded` is available as an attribute on
+the :class:`_postgresql.Insert` object; this object is a
+:class:`_expression.ColumnCollection`
+which alias contains all columns of the target
+table:
+
+.. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(
+    ...     id='some_id',
+    ...     data='inserted value',
+    ...     author='jlh'
+    ... )
+    >>> do_update_stmt = stmt.on_conflict_do_update(
+    ...     index_elements=['id'],
+    ...     set_=dict(data='updated value', author=stmt.excluded.author)
+    ... )
+    >>> print(do_update_stmt)
+    {opensql}INSERT INTO my_table (id, data, author)
+    VALUES (%(id)s, %(data)s, %(author)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author
+
+Additional WHERE Criteria
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The :meth:`_expression.Insert.on_conflict_do_update` method also accepts
+a WHERE clause using the :paramref:`_postgresql.Insert.on_conflict_do_update.where`
+parameter, which will limit those rows which receive an UPDATE:
+
+.. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(
+    ...     id='some_id',
+    ...     data='inserted value',
+    ...     author='jlh'
+    ... )
+    >>> on_update_stmt = stmt.on_conflict_do_update(
+    ...     index_elements=['id'],
+    ...     set_=dict(data='updated value', author=stmt.excluded.author),
+    ...     where=(my_table.c.status == 2)
+    ... )
+    >>> print(on_update_stmt)
+    {opensql}INSERT INTO my_table (id, data, author)
+    VALUES (%(id)s, %(data)s, %(author)s)
+    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author
+    WHERE my_table.status = %(status_1)s
+
+Skipping Rows with DO NOTHING
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``ON CONFLICT`` may be used to skip inserting a row entirely
+if any conflict with a unique or exclusion constraint occurs; below
+this is illustrated using the
+:meth:`~.postgresql.Insert.on_conflict_do_nothing` method:
+
+.. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(id='some_id', data='inserted value')
+    >>> stmt = stmt.on_conflict_do_nothing(index_elements=['id'])
+    >>> print(stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT (id) DO NOTHING
+
+If ``DO NOTHING`` is used without specifying any columns or constraint,
+it has the effect of skipping the INSERT for any unique or exclusion
+constraint violation which occurs:
+
+.. sourcecode:: pycon+sql
+
+    >>> stmt = insert(my_table).values(id='some_id', data='inserted value')
+    >>> stmt = stmt.on_conflict_do_nothing()
+    >>> print(stmt)
+    {opensql}INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
+    ON CONFLICT DO NOTHING
+
+.. _postgresql_match:
+
+Full Text Search
+----------------
+
+SQLAlchemy makes available the PostgreSQL ``@@`` operator via the
+:meth:`_expression.ColumnElement.match` method on any textual column expression.
+
+On the PostgreSQL dialect, an expression like the following::
+
+    select(sometable.c.text.match("search string"))
+
+will emit to the database::
+
+    SELECT text @@ to_tsquery('search string') FROM table
+
+Various other PostgreSQL text search functions such as ``to_tsquery()``,
+``to_tsvector()``, and ``plainto_tsquery()`` are available by explicitly using
+the standard SQLAlchemy :data:`.func` construct.
+
+For example::
+
+    select(func.to_tsvector('fat cats ate rats').match('cat & rat'))
+
+Emits the equivalent of::
+
+    SELECT to_tsvector('fat cats ate rats') @@ to_tsquery('cat & rat')
+
+The :class:`_postgresql.TSVECTOR` type can provide for explicit CAST::
+
+    from sqlalchemy.dialects.postgresql import TSVECTOR
+    from sqlalchemy import select, cast
+    select(cast("some text", TSVECTOR))
+
+produces a statement equivalent to::
+
+    SELECT CAST('some text' AS TSVECTOR) AS anon_1
+
+.. tip::
+
+    It's important to remember that text searching in PostgreSQL is powerful but complicated,
+    and SQLAlchemy users are advised to reference the PostgreSQL documentation
+    regarding
+    `Full Text Search <https://www.postgresql.org/docs/current/textsearch-controls.html>`_.
+
+    There are important differences between ``to_tsquery`` and
+    ``plainto_tsquery``, the most significant of which is that ``to_tsquery``
+    expects specially formatted "querytext" that is written to PostgreSQL's own
+    specification, while ``plainto_tsquery`` expects unformatted text that is
+    transformed into ``to_tsquery`` compatible querytext. This means the input to
+    ``.match()`` under PostgreSQL may be incompatible with the input to
+    ``.match()`` under another database backend. SQLAlchemy users who support
+    multiple backends are advised to carefully implement their usage of
+    ``.match()`` to work around these constraints.
+
+Full Text Searches in PostgreSQL are influenced by a combination of: the
+PostgreSQL setting of ``default_text_search_config``, the ``regconfig`` used
+to build the GIN/GiST indexes, and the ``regconfig`` optionally passed in
+during a query.
+
+When performing a Full Text Search against a column that has a GIN or
+GiST index that is already pre-computed (which is common on full text
+searches) one may need to explicitly pass in a particular PostgreSQL
+``regconfig`` value to ensure the query-planner utilizes the index and does
+not re-compute the column on demand.
+
+In order to provide for this explicit query planning, or to use different
+search strategies, the ``match`` method accepts a ``postgresql_regconfig``
+keyword argument::
+
+    select(mytable.c.id).where(
+        mytable.c.title.match('somestring', postgresql_regconfig='english')
+    )
+
+Emits the equivalent of::
+
+    SELECT mytable.id FROM mytable
+    WHERE mytable.title @@ to_tsquery('english', 'somestring')
+
+One can also specifically pass in a `'regconfig'` value to the
+``to_tsvector()`` command as the initial argument::
+
+    select(mytable.c.id).where(
+            func.to_tsvector('english', mytable.c.title )\
+            .match('somestring', postgresql_regconfig='english')
+        )
+
+produces a statement equivalent to::
+
+    SELECT mytable.id FROM mytable
+    WHERE to_tsvector('english', mytable.title) @@
+        to_tsquery('english', 'somestring')
+
+It is recommended that you use the ``EXPLAIN ANALYZE...`` tool from
+PostgreSQL to ensure that you are generating queries with SQLAlchemy that
+take full advantage of any indexes you may have created for full text search.
+
+.. seealso::
+
+    `Full Text Search <https://www.postgresql.org/docs/current/textsearch-controls.html>`_ - in the PostgreSQL documentation
+
+
+FROM ONLY ...
+-------------
+
+The dialect supports PostgreSQL's ONLY keyword for targeting only a particular
+table in an inheritance hierarchy. This can be used to produce the
+``SELECT ... FROM ONLY``, ``UPDATE ONLY ...``, and ``DELETE FROM ONLY ...``
+syntaxes. It uses SQLAlchemy's hints mechanism::
+
+    # SELECT ... FROM ONLY ...
+    result = table.select().with_hint(table, 'ONLY', 'postgresql')
+    print(result.fetchall())
+
+    # UPDATE ONLY ...
+    table.update(values=dict(foo='bar')).with_hint('ONLY',
+                                                   dialect_name='postgresql')
+
+    # DELETE FROM ONLY ...
+    table.delete().with_hint('ONLY', dialect_name='postgresql')
+
+
+.. _postgresql_indexes:
+
+PostgreSQL-Specific Index Options
+---------------------------------
+
+Several extensions to the :class:`.Index` construct are available, specific
+to the PostgreSQL dialect.
+
+Covering Indexes
+^^^^^^^^^^^^^^^^
+
+The ``postgresql_include`` option renders INCLUDE(colname) for the given
+string names::
+
+    Index("my_index", table.c.x, postgresql_include=['y'])
+
+would render the index as ``CREATE INDEX my_index ON table (x) INCLUDE (y)``
+
+Note that this feature requires PostgreSQL 11 or later.
+
+.. versionadded:: 1.4
+
+.. _postgresql_partial_indexes:
+
+Partial Indexes
+^^^^^^^^^^^^^^^
+
+Partial indexes add criterion to the index definition so that the index is
+applied to a subset of rows.   These can be specified on :class:`.Index`
+using the ``postgresql_where`` keyword argument::
+
+  Index('my_index', my_table.c.id, postgresql_where=my_table.c.value > 10)
+
+.. _postgresql_operator_classes:
+
+Operator Classes
+^^^^^^^^^^^^^^^^
+
+PostgreSQL allows the specification of an *operator class* for each column of
+an index (see
+https://www.postgresql.org/docs/current/interactive/indexes-opclass.html).
+The :class:`.Index` construct allows these to be specified via the
+``postgresql_ops`` keyword argument::
+
+    Index(
+        'my_index', my_table.c.id, my_table.c.data,
+        postgresql_ops={
+            'data': 'text_pattern_ops',
+            'id': 'int4_ops'
+        })
+
+Note that the keys in the ``postgresql_ops`` dictionaries are the
+"key" name of the :class:`_schema.Column`, i.e. the name used to access it from
+the ``.c`` collection of :class:`_schema.Table`, which can be configured to be
+different than the actual name of the column as expressed in the database.
+
+If ``postgresql_ops`` is to be used against a complex SQL expression such
+as a function call, then to apply to the column it must be given a label
+that is identified in the dictionary by name, e.g.::
+
+    Index(
+        'my_index', my_table.c.id,
+        func.lower(my_table.c.data).label('data_lower'),
+        postgresql_ops={
+            'data_lower': 'text_pattern_ops',
+            'id': 'int4_ops'
+        })
+
+Operator classes are also supported by the
+:class:`_postgresql.ExcludeConstraint` construct using the
+:paramref:`_postgresql.ExcludeConstraint.ops` parameter. See that parameter for
+details.
+
+.. versionadded:: 1.3.21 added support for operator classes with
+   :class:`_postgresql.ExcludeConstraint`.
+
+
+Index Types
+^^^^^^^^^^^
+
+PostgreSQL provides several index types: B-Tree, Hash, GiST, and GIN, as well
+as the ability for users to create their own (see
+https://www.postgresql.org/docs/current/static/indexes-types.html). These can be
+specified on :class:`.Index` using the ``postgresql_using`` keyword argument::
+
+    Index('my_index', my_table.c.data, postgresql_using='gin')
+
+The value passed to the keyword argument will be simply passed through to the
+underlying CREATE INDEX command, so it *must* be a valid index type for your
+version of PostgreSQL.
+
+.. _postgresql_index_storage:
+
+Index Storage Parameters
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+PostgreSQL allows storage parameters to be set on indexes. The storage
+parameters available depend on the index method used by the index. Storage
+parameters can be specified on :class:`.Index` using the ``postgresql_with``
+keyword argument::
+
+    Index('my_index', my_table.c.data, postgresql_with={"fillfactor": 50})
+
+.. versionadded:: 1.0.6
+
+PostgreSQL allows to define the tablespace in which to create the index.
+The tablespace can be specified on :class:`.Index` using the
+``postgresql_tablespace`` keyword argument::
+
+    Index('my_index', my_table.c.data, postgresql_tablespace='my_tablespace')
+
+.. versionadded:: 1.1
+
+Note that the same option is available on :class:`_schema.Table` as well.
+
+.. _postgresql_index_concurrently:
+
+Indexes with CONCURRENTLY
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The PostgreSQL index option CONCURRENTLY is supported by passing the
+flag ``postgresql_concurrently`` to the :class:`.Index` construct::
+
+    tbl = Table('testtbl', m, Column('data', Integer))
+
+    idx1 = Index('test_idx1', tbl.c.data, postgresql_concurrently=True)
+
+The above index construct will render DDL for CREATE INDEX, assuming
+PostgreSQL 8.2 or higher is detected or for a connection-less dialect, as::
+
+    CREATE INDEX CONCURRENTLY test_idx1 ON testtbl (data)
+
+For DROP INDEX, assuming PostgreSQL 9.2 or higher is detected or for
+a connection-less dialect, it will emit::
+
+    DROP INDEX CONCURRENTLY test_idx1
+
+.. versionadded:: 1.1 support for CONCURRENTLY on DROP INDEX.  The
+   CONCURRENTLY keyword is now only emitted if a high enough version
+   of PostgreSQL is detected on the connection (or for a connection-less
+   dialect).
+
+When using CONCURRENTLY, the PostgreSQL database requires that the statement
+be invoked outside of a transaction block.   The Python DBAPI enforces that
+even for a single statement, a transaction is present, so to use this
+construct, the DBAPI's "autocommit" mode must be used::
+
+    metadata = MetaData()
+    table = Table(
+        "foo", metadata,
+        Column("id", String))
+    index = Index(
+        "foo_idx", table.c.id, postgresql_concurrently=True)
+
+    with engine.connect() as conn:
+        with conn.execution_options(isolation_level='AUTOCOMMIT'):
+            table.create(conn)
+
+.. seealso::
+
+    :ref:`postgresql_isolation_level`
+
+.. _postgresql_index_reflection:
+
+PostgreSQL Index Reflection
+---------------------------
+
+The PostgreSQL database creates a UNIQUE INDEX implicitly whenever the
+UNIQUE CONSTRAINT construct is used.   When inspecting a table using
+:class:`_reflection.Inspector`, the :meth:`_reflection.Inspector.get_indexes`
+and the :meth:`_reflection.Inspector.get_unique_constraints`
+will report on these
+two constructs distinctly; in the case of the index, the key
+``duplicates_constraint`` will be present in the index entry if it is
+detected as mirroring a constraint.   When performing reflection using
+``Table(..., autoload_with=engine)``, the UNIQUE INDEX is **not** returned
+in :attr:`_schema.Table.indexes` when it is detected as mirroring a
+:class:`.UniqueConstraint` in the :attr:`_schema.Table.constraints` collection
+.
+
+.. versionchanged:: 1.0.0 - :class:`_schema.Table` reflection now includes
+   :class:`.UniqueConstraint` objects present in the
+   :attr:`_schema.Table.constraints`
+   collection; the PostgreSQL backend will no longer include a "mirrored"
+   :class:`.Index` construct in :attr:`_schema.Table.indexes`
+   if it is detected
+   as corresponding to a unique constraint.
+
+Special Reflection Options
+--------------------------
+
+The :class:`_reflection.Inspector`
+used for the PostgreSQL backend is an instance
+of :class:`.PGInspector`, which offers additional methods::
+
+    from sqlalchemy import create_engine, inspect
+
+    engine = create_engine("postgresql+psycopg2://localhost/test")
+    insp = inspect(engine)  # will be a PGInspector
+
+    print(insp.get_enums())
+
+.. autoclass:: PGInspector
+    :members:
+
+.. _postgresql_table_options:
+
+PostgreSQL Table Options
+------------------------
+
+Several options for CREATE TABLE are supported directly by the PostgreSQL
+dialect in conjunction with the :class:`_schema.Table` construct:
+
+* ``TABLESPACE``::
+
+    Table("some_table", metadata, ..., postgresql_tablespace='some_tablespace')
+
+  The above option is also available on the :class:`.Index` construct.
+
+* ``ON COMMIT``::
+
+    Table("some_table", metadata, ..., postgresql_on_commit='PRESERVE ROWS')
+
+* ``WITH OIDS``::
+
+    Table("some_table", metadata, ..., postgresql_with_oids=True)
+
+* ``WITHOUT OIDS``::
+
+    Table("some_table", metadata, ..., postgresql_with_oids=False)
+
+* ``INHERITS``::
+
+    Table("some_table", metadata, ..., postgresql_inherits="some_supertable")
+
+    Table("some_table", metadata, ..., postgresql_inherits=("t1", "t2", ...))
+
+    .. versionadded:: 1.0.0
+
+* ``PARTITION BY``::
+
+    Table("some_table", metadata, ...,
+          postgresql_partition_by='LIST (part_column)')
+
+    .. versionadded:: 1.2.6
+
+.. seealso::
+
+    `PostgreSQL CREATE TABLE options
+    <https://www.postgresql.org/docs/current/static/sql-createtable.html>`_ -
+    in the PostgreSQL documentation.
+
+.. _postgresql_constraint_options:
+
+PostgreSQL Constraint Options
+-----------------------------
+
+The following option(s) are supported by the PostgreSQL dialect in conjunction
+with selected constraint constructs:
+
+* ``NOT VALID``:  This option applies towards CHECK and FOREIGN KEY constraints
+  when the constraint is being added to an existing table via ALTER TABLE,
+  and has the effect that existing rows are not scanned during the ALTER
+  operation against the constraint being added.
+
+  When using a SQL migration tool such as `Alembic <https://alembic.sqlalchemy.org>`_
+  that renders ALTER TABLE constructs, the ``postgresql_not_valid`` argument
+  may be specified as an additional keyword argument within the operation
+  that creates the constraint, as in the following Alembic example::
+
+        def update():
+            op.create_foreign_key(
+                "fk_user_address",
+                "address",
+                "user",
+                ["user_id"],
+                ["id"],
+                postgresql_not_valid=True
+            )
+
+  The keyword is ultimately accepted directly by the
+  :class:`_schema.CheckConstraint`, :class:`_schema.ForeignKeyConstraint`
+  and :class:`_schema.ForeignKey` constructs; when using a tool like
+  Alembic, dialect-specific keyword arguments are passed through to
+  these constructs from the migration operation directives::
+
+       CheckConstraint("some_field IS NOT NULL", postgresql_not_valid=True)
+
+       ForeignKeyConstraint(["some_id"], ["some_table.some_id"], postgresql_not_valid=True)
+
+  .. versionadded:: 1.4.32
+
+  .. seealso::
+
+      `PostgreSQL ALTER TABLE options
+      <https://www.postgresql.org/docs/current/static/sql-altertable.html>`_ -
+      in the PostgreSQL documentation.
+
+.. _postgresql_table_valued_overview:
+
+Table values, Table and Column valued functions, Row and Tuple objects
+-----------------------------------------------------------------------
+
+PostgreSQL makes great use of modern SQL forms such as table-valued functions,
+tables and rows as values.   These constructs are commonly used as part
+of PostgreSQL's support for complex datatypes such as JSON, ARRAY, and other
+datatypes.  SQLAlchemy's SQL expression language has native support for
+most table-valued and row-valued forms.
+
+.. _postgresql_table_valued:
+
+Table-Valued Functions
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Many PostgreSQL built-in functions are intended to be used in the FROM clause
+of a SELECT statement, and are capable of returning table rows or sets of table
+rows. A large portion of PostgreSQL's JSON functions for example such as
+``json_array_elements()``, ``json_object_keys()``, ``json_each_text()``,
+``json_each()``, ``json_to_record()``, ``json_populate_recordset()`` use such
+forms. These classes of SQL function calling forms in SQLAlchemy are available
+using the :meth:`_functions.FunctionElement.table_valued` method in conjunction
+with :class:`_functions.Function` objects generated from the :data:`_sql.func`
+namespace.
+
+Examples from PostgreSQL's reference documentation follow below:
+
+* ``json_each()``::
+
+    >>> from sqlalchemy import select, func
+    >>> stmt = select(func.json_each('{"a":"foo", "b":"bar"}').table_valued("key", "value"))
+    >>> print(stmt)
+    SELECT anon_1.key, anon_1.value
+    FROM json_each(:json_each_1) AS anon_1
+
+* ``json_populate_record()``::
+
+    >>> from sqlalchemy import select, func, literal_column
+    >>> stmt = select(
+    ...     func.json_populate_record(
+    ...         literal_column("null::myrowtype"),
+    ...         '{"a":1,"b":2}'
+    ...     ).table_valued("a", "b", name="x")
+    ... )
+    >>> print(stmt)
+    SELECT x.a, x.b
+    FROM json_populate_record(null::myrowtype, :json_populate_record_1) AS x
+
+* ``json_to_record()`` - this form uses a PostgreSQL specific form of derived
+  columns in the alias, where we may make use of :func:`_sql.column` elements with
+  types to produce them.  The :meth:`_functions.FunctionElement.table_valued`
+  method produces  a :class:`_sql.TableValuedAlias` construct, and the method
+  :meth:`_sql.TableValuedAlias.render_derived` method sets up the derived
+  columns specification::
+
+    >>> from sqlalchemy import select, func, column, Integer, Text
+    >>> stmt = select(
+    ...     func.json_to_record('{"a":1,"b":[1,2,3],"c":"bar"}').table_valued(
+    ...         column("a", Integer), column("b", Text), column("d", Text),
+    ...     ).render_derived(name="x", with_types=True)
+    ... )
+    >>> print(stmt)
+    SELECT x.a, x.b, x.d
+    FROM json_to_record(:json_to_record_1) AS x(a INTEGER, b TEXT, d TEXT)
+
+* ``WITH ORDINALITY`` - part of the SQL standard, ``WITH ORDINALITY`` adds an
+  ordinal counter to the output of a function and is accepted by a limited set
+  of PostgreSQL functions including ``unnest()`` and ``generate_series()``. The
+  :meth:`_functions.FunctionElement.table_valued` method accepts a keyword
+  parameter ``with_ordinality`` for this purpose, which accepts the string name
+  that will be applied to the "ordinality" column::
+
+    >>> from sqlalchemy import select, func
+    >>> stmt = select(
+    ...     func.generate_series(4, 1, -1).
+    ...     table_valued("value", with_ordinality="ordinality").
+    ...     render_derived()
+    ... )
+    >>> print(stmt)
+    SELECT anon_1.value, anon_1.ordinality
+    FROM generate_series(:generate_series_1, :generate_series_2, :generate_series_3)
+    WITH ORDINALITY AS anon_1(value, ordinality)
+
+.. versionadded:: 1.4.0b2
+
+.. seealso::
+
+    :ref:`tutorial_functions_table_valued` - in the :ref:`unified_tutorial`
+
+.. _postgresql_column_valued:
+
+Column Valued Functions
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Similar to the table valued function, a column valued function is present
+in the FROM clause, but delivers itself to the columns clause as a single
+scalar value.  PostgreSQL functions such as ``json_array_elements()``,
+``unnest()`` and ``generate_series()`` may use this form. Column valued functions are available using the
+:meth:`_functions.FunctionElement.column_valued` method of :class:`_functions.FunctionElement`:
+
+* ``json_array_elements()``::
+
+    >>> from sqlalchemy import select, func
+    >>> stmt = select(func.json_array_elements('["one", "two"]').column_valued("x"))
+    >>> print(stmt)
+    SELECT x
+    FROM json_array_elements(:json_array_elements_1) AS x
+
+* ``unnest()`` - in order to generate a PostgreSQL ARRAY literal, the
+  :func:`_postgresql.array` construct may be used::
+
+
+    >>> from sqlalchemy.dialects.postgresql import array
+    >>> from sqlalchemy import select, func
+    >>> stmt = select(func.unnest(array([1, 2])).column_valued())
+    >>> print(stmt)
+    SELECT anon_1
+    FROM unnest(ARRAY[%(param_1)s, %(param_2)s]) AS anon_1
+
+  The function can of course be used against an existing table-bound column
+  that's of type :class:`_types.ARRAY`::
+
+    >>> from sqlalchemy import table, column, ARRAY, Integer
+    >>> from sqlalchemy import select, func
+    >>> t = table("t", column('value', ARRAY(Integer)))
+    >>> stmt = select(func.unnest(t.c.value).column_valued("unnested_value"))
+    >>> print(stmt)
+    SELECT unnested_value
+    FROM unnest(t.value) AS unnested_value
+
+.. seealso::
+
+    :ref:`tutorial_functions_column_valued` - in the :ref:`unified_tutorial`
+
+
+Row Types
+^^^^^^^^^
+
+Built-in support for rendering a ``ROW`` may be approximated using
+``func.ROW`` with the :attr:`_sa.func` namespace, or by using the
+:func:`_sql.tuple_` construct::
+
+    >>> from sqlalchemy import table, column, func, tuple_
+    >>> t = table("t", column("id"), column("fk"))
+    >>> stmt = t.select().where(
+    ...     tuple_(t.c.id, t.c.fk) > (1,2)
+    ... ).where(
+    ...     func.ROW(t.c.id, t.c.fk) < func.ROW(3, 7)
+    ... )
+    >>> print(stmt)
+    SELECT t.id, t.fk
+    FROM t
+    WHERE (t.id, t.fk) > (:param_1, :param_2) AND ROW(t.id, t.fk) < ROW(:ROW_1, :ROW_2)
+
+.. seealso::
+
+    `PostgreSQL Row Constructors
+    <https://www.postgresql.org/docs/current/sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS>`_
+
+    `PostgreSQL Row Constructor Comparison
+    <https://www.postgresql.org/docs/current/functions-comparisons.html#ROW-WISE-COMPARISON>`_
+
+Table Types passed to Functions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+PostgreSQL supports passing a table as an argument to a function, which it
+refers towards as a "record" type. SQLAlchemy :class:`_sql.FromClause` objects
+such as :class:`_schema.Table` support this special form using the
+:meth:`_sql.FromClause.table_valued` method, which is comparable to the
+:meth:`_functions.FunctionElement.table_valued` method except that the collection
+of columns is already established by that of the :class:`_sql.FromClause`
+itself::
+
+
+    >>> from sqlalchemy import table, column, func, select
+    >>> a = table( "a", column("id"), column("x"), column("y"))
+    >>> stmt = select(func.row_to_json(a.table_valued()))
+    >>> print(stmt)
+    SELECT row_to_json(a) AS row_to_json_1
+    FROM a
+
+.. versionadded:: 1.4.0b2
+
+
+ARRAY Types
+-----------
+
+The PostgreSQL dialect supports arrays, both as multidimensional column types
+as well as array literals:
+
+* :class:`_postgresql.ARRAY` - ARRAY datatype
+
+* :class:`_postgresql.array` - array literal
+
+* :func:`_postgresql.array_agg` - ARRAY_AGG SQL function
+
+* :class:`_postgresql.aggregate_order_by` - helper for PG's ORDER BY aggregate
+  function syntax.
+
+JSON Types
+----------
+
+The PostgreSQL dialect supports both JSON and JSONB datatypes, including
+psycopg2's native support and support for all of PostgreSQL's special
+operators:
+
+* :class:`_postgresql.JSON`
+
+* :class:`_postgresql.JSONB`
+
+HSTORE Type
+-----------
+
+The PostgreSQL HSTORE type as well as hstore literals are supported:
+
+* :class:`_postgresql.HSTORE` - HSTORE datatype
+
+* :class:`_postgresql.hstore` - hstore literal
+
+ENUM Types
+----------
+
+PostgreSQL has an independently creatable TYPE structure which is used
+to implement an enumerated type.   This approach introduces significant
+complexity on the SQLAlchemy side in terms of when this type should be
+CREATED and DROPPED.   The type object is also an independently reflectable
+entity.   The following sections should be consulted:
+
+* :class:`_postgresql.ENUM` - DDL and typing support for ENUM.
+
+* :meth:`.PGInspector.get_enums` - retrieve a listing of current ENUM types
+
+* :meth:`.postgresql.ENUM.create` , :meth:`.postgresql.ENUM.drop` - individual
+  CREATE and DROP commands for ENUM.
+
+.. _postgresql_array_of_enum:
+
+Using ENUM with ARRAY
+^^^^^^^^^^^^^^^^^^^^^
+
+The combination of ENUM and ARRAY is not directly supported by backend
+DBAPIs at this time.   Prior to SQLAlchemy 1.3.17, a special workaround
+was needed in order to allow this combination to work, described below.
+
+.. versionchanged:: 1.3.17 The combination of ENUM and ARRAY is now directly
+   handled by SQLAlchemy's implementation without any workarounds needed.
+
+.. sourcecode:: python
+
+    from sqlalchemy import TypeDecorator
+    from sqlalchemy.dialects.postgresql import ARRAY
+
+    class ArrayOfEnum(TypeDecorator):
+        impl = ARRAY
+
+        def bind_expression(self, bindvalue):
+            return sa.cast(bindvalue, self)
+
+        def result_processor(self, dialect, coltype):
+            super_rp = super(ArrayOfEnum, self).result_processor(
+                dialect, coltype)
+
+            def handle_raw_string(value):
+                inner = re.match(r"^{(.*)}$", value).group(1)
+                return inner.split(",") if inner else []
+
+            def process(value):
+                if value is None:
+                    return None
+                return super_rp(handle_raw_string(value))
+            return process
+
+E.g.::
+
+    Table(
+        'mydata', metadata,
+        Column('id', Integer, primary_key=True),
+        Column('data', ArrayOfEnum(ENUM('a', 'b, 'c', name='myenum')))
+
+    )
+
+This type is not included as a built-in type as it would be incompatible
+with a DBAPI that suddenly decides to support ARRAY of ENUM directly in
+a new version.
+
+.. _postgresql_array_of_json:
+
+Using JSON/JSONB with ARRAY
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Similar to using ENUM, prior to SQLAlchemy 1.3.17, for an ARRAY of JSON/JSONB
+we need to render the appropriate CAST.   Current psycopg2 drivers accommodate
+the result set correctly without any special steps.
+
+.. versionchanged:: 1.3.17 The combination of JSON/JSONB and ARRAY is now
+   directly handled by SQLAlchemy's implementation without any workarounds
+   needed.
+
+.. sourcecode:: python
+
+    class CastingArray(ARRAY):
+        def bind_expression(self, bindvalue):
+            return sa.cast(bindvalue, self)
+
+E.g.::
+
+    Table(
+        'mydata', metadata,
+        Column('id', Integer, primary_key=True),
+        Column('data', CastingArray(JSONB))
+    )
+
+
+"""  # noqa: E501
+
+from collections import defaultdict
+import datetime as dt
+import re
+from uuid import UUID as _python_UUID
+
+from . import array as _array
+from . import dml
+from . import hstore as _hstore
+from . import json as _json
+from . import ranges as _ranges
+from ... import exc
+from ... import schema
+from ... import sql
+from ... import util
+from ...engine import characteristics
+from ...engine import default
+from ...engine import reflection
+from ...sql import coercions
+from ...sql import compiler
+from ...sql import elements
+from ...sql import expression
+from ...sql import roles
+from ...sql import sqltypes
+from ...sql import util as sql_util
+from ...sql.ddl import DDLBase
+from ...types import BIGINT
+from ...types import BOOLEAN
+from ...types import CHAR
+from ...types import DATE
+from ...types import FLOAT
+from ...types import INTEGER
+from ...types import NUMERIC
+from ...types import REAL
+from ...types import SMALLINT
+from ...types import TEXT
+from ...types import VARCHAR
+
+IDX_USING = re.compile(r"^(?:btree|hash|gist|gin|[\w_]+)$", re.I)
+
+AUTOCOMMIT_REGEXP = re.compile(
+    r"\s*(?:UPDATE|INSERT|CREATE|DELETE|DROP|ALTER|GRANT|REVOKE|"
+    "IMPORT FOREIGN SCHEMA|REFRESH MATERIALIZED VIEW|TRUNCATE)",
+    re.I | re.UNICODE,
+)
+
+RESERVED_WORDS = set(
+    [
+        "all",
+        "analyse",
+        "analyze",
+        "and",
+        "any",
+        "array",
+        "as",
+        "asc",
+        "asymmetric",
+        "both",
+        "case",
+        "cast",
+        "check",
+        "collate",
+        "column",
+        "constraint",
+        "create",
+        "current_catalog",
+        "current_date",
+        "current_role",
+        "current_time",
+        "current_timestamp",
+        "current_user",
+        "default",
+        "deferrable",
+        "desc",
+        "distinct",
+        "do",
+        "else",
+        "end",
+        "except",
+        "false",
+        "fetch",
+        "for",
+        "foreign",
+        "from",
+        "grant",
+        "group",
+        "having",
+        "in",
+        "initially",
+        "intersect",
+        "into",
+        "leading",
+        "limit",
+        "localtime",
+        "localtimestamp",
+        "new",
+        "not",
+        "null",
+        "of",
+        "off",
+        "offset",
+        "old",
+        "on",
+        "only",
+        "or",
+        "order",
+        "placing",
+        "primary",
+        "references",
+        "returning",
+        "select",
+        "session_user",
+        "some",
+        "symmetric",
+        "table",
+        "then",
+        "to",
+        "trailing",
+        "true",
+        "union",
+        "unique",
+        "user",
+        "using",
+        "variadic",
+        "when",
+        "where",
+        "window",
+        "with",
+        "authorization",
+        "between",
+        "binary",
+        "cross",
+        "current_schema",
+        "freeze",
+        "full",
+        "ilike",
+        "inner",
+        "is",
+        "isnull",
+        "join",
+        "left",
+        "like",
+        "natural",
+        "notnull",
+        "outer",
+        "over",
+        "overlaps",
+        "right",
+        "similar",
+        "verbose",
+    ]
+)
+
+_DECIMAL_TYPES = (1231, 1700)
+_FLOAT_TYPES = (700, 701, 1021, 1022)
+_INT_TYPES = (20, 21, 23, 26, 1005, 1007, 1016)
+
+
+class BYTEA(sqltypes.LargeBinary):
+    __visit_name__ = "BYTEA"
+
+
+class DOUBLE_PRECISION(sqltypes.Float):
+    __visit_name__ = "DOUBLE_PRECISION"
+
+
+class INET(sqltypes.TypeEngine):
+    __visit_name__ = "INET"
+
+
+PGInet = INET
+
+
+class CIDR(sqltypes.TypeEngine):
+    __visit_name__ = "CIDR"
+
+
+PGCidr = CIDR
+
+
+class MACADDR(sqltypes.TypeEngine):
+    __visit_name__ = "MACADDR"
+
+
+PGMacAddr = MACADDR
+
+
+class MONEY(sqltypes.TypeEngine):
+
+    r"""Provide the PostgreSQL MONEY type.
+
+    Depending on driver, result rows using this type may return a
+    string value which includes currency symbols.
+
+    For this reason, it may be preferable to provide conversion to a
+    numerically-based currency datatype using :class:`_types.TypeDecorator`::
+
+        import re
+        import decimal
+        from sqlalchemy import TypeDecorator
+
+        class NumericMoney(TypeDecorator):
+            impl = MONEY
+
+            def process_result_value(self, value: Any, dialect: Any) -> None:
+                if value is not None:
+                    # adjust this for the currency and numeric
+                    m = re.match(r"\$([\d.]+)", value)
+                    if m:
+                        value = decimal.Decimal(m.group(1))
+                return value
+
+    Alternatively, the conversion may be applied as a CAST using
+    the :meth:`_types.TypeDecorator.column_expression` method as follows::
+
+        import decimal
+        from sqlalchemy import cast
+        from sqlalchemy import TypeDecorator
+
+        class NumericMoney(TypeDecorator):
+            impl = MONEY
+
+            def column_expression(self, column: Any):
+                return cast(column, Numeric())
+
+    .. versionadded:: 1.2
+
+    """
+
+    __visit_name__ = "MONEY"
+
+
+class OID(sqltypes.TypeEngine):
+
+    """Provide the PostgreSQL OID type.
+
+    .. versionadded:: 0.9.5
+
+    """
+
+    __visit_name__ = "OID"
+
+
+class REGCLASS(sqltypes.TypeEngine):
+
+    """Provide the PostgreSQL REGCLASS type.
+
+    .. versionadded:: 1.2.7
+
+    """
+
+    __visit_name__ = "REGCLASS"
+
+
+class TIMESTAMP(sqltypes.TIMESTAMP):
+
+    """Provide the PostgreSQL TIMESTAMP type."""
+
+    __visit_name__ = "TIMESTAMP"
+
+    def __init__(self, timezone=False, precision=None):
+        """Construct a TIMESTAMP.
+
+        :param timezone: boolean value if timezone present, default False
+        :param precision: optional integer precision value
+
+         .. versionadded:: 1.4
+
+        """
+        super(TIMESTAMP, self).__init__(timezone=timezone)
+        self.precision = precision
+
+
+class TIME(sqltypes.TIME):
+
+    """PostgreSQL TIME type."""
+
+    __visit_name__ = "TIME"
+
+    def __init__(self, timezone=False, precision=None):
+        """Construct a TIME.
+
+        :param timezone: boolean value if timezone present, default False
+        :param precision: optional integer precision value
+
+         .. versionadded:: 1.4
+
+        """
+        super(TIME, self).__init__(timezone=timezone)
+        self.precision = precision
+
+
+class INTERVAL(sqltypes.NativeForEmulated, sqltypes._AbstractInterval):
+
+    """PostgreSQL INTERVAL type."""
+
+    __visit_name__ = "INTERVAL"
+    native = True
+
+    def __init__(self, precision=None, fields=None):
+        """Construct an INTERVAL.
+
+        :param precision: optional integer precision value
+        :param fields: string fields specifier.  allows storage of fields
+         to be limited, such as ``"YEAR"``, ``"MONTH"``, ``"DAY TO HOUR"``,
+         etc.
+
+         .. versionadded:: 1.2
+
+        """
+        self.precision = precision
+        self.fields = fields
+
+    @classmethod
+    def adapt_emulated_to_native(cls, interval, **kw):
+        return INTERVAL(precision=interval.second_precision)
+
+    @property
+    def _type_affinity(self):
+        return sqltypes.Interval
+
+    def as_generic(self, allow_nulltype=False):
+        return sqltypes.Interval(native=True, second_precision=self.precision)
+
+    @property
+    def python_type(self):
+        return dt.timedelta
+
+    def coerce_compared_value(self, op, value):
+        return self
+
+
+PGInterval = INTERVAL
+
+
+class BIT(sqltypes.TypeEngine):
+    __visit_name__ = "BIT"
+
+    def __init__(self, length=None, varying=False):
+        if not varying:
+            # BIT without VARYING defaults to length 1
+            self.length = length or 1
+        else:
+            # but BIT VARYING can be unlimited-length, so no default
+            self.length = length
+        self.varying = varying
+
+
+PGBit = BIT
+
+
+class UUID(sqltypes.TypeEngine):
+
+    """PostgreSQL UUID type.
+
+    Represents the UUID column type, interpreting
+    data either as natively returned by the DBAPI
+    or as Python uuid objects.
+
+    The UUID type is currently known to work within the prominent DBAPI
+    drivers supported by SQLAlchemy including psycopg2, pg8000 and
+    asyncpg. Support for other DBAPI drivers may be incomplete or non-present.
+
+    """
+
+    __visit_name__ = "UUID"
+
+    def __init__(self, as_uuid=False):
+        """Construct a UUID type.
+
+
+        :param as_uuid=False: if True, values will be interpreted
+         as Python uuid objects, converting to/from string via the
+         DBAPI.
+
+        """
+        self.as_uuid = as_uuid
+
+    def coerce_compared_value(self, op, value):
+        """See :meth:`.TypeEngine.coerce_compared_value` for a description."""
+
+        if isinstance(value, util.string_types):
+            return self
+        else:
+            return super(UUID, self).coerce_compared_value(op, value)
+
+    def bind_processor(self, dialect):
+        if self.as_uuid:
+
+            def process(value):
+                if value is not None:
+                    value = util.text_type(value)
+                return value
+
+            return process
+        else:
+            return None
+
+    def result_processor(self, dialect, coltype):
+        if self.as_uuid:
+
+            def process(value):
+                if value is not None:
+                    value = _python_UUID(value)
+                return value
+
+            return process
+        else:
+            return None
+
+    def literal_processor(self, dialect):
+        if self.as_uuid:
+
+            def process(value):
+                if value is not None:
+                    value = "'%s'::UUID" % value
+                return value
+
+            return process
+        else:
+
+            def process(value):
+                if value is not None:
+                    value = "'%s'" % value
+                return value
+
+            return process
+
+    @property
+    def python_type(self):
+        return _python_UUID if self.as_uuid else str
+
+
+PGUuid = UUID
+
+
+class TSVECTOR(sqltypes.TypeEngine):
+
+    """The :class:`_postgresql.TSVECTOR` type implements the PostgreSQL
+    text search type TSVECTOR.
+
+    It can be used to do full text queries on natural language
+    documents.
+
+    .. versionadded:: 0.9.0
+
+    .. seealso::
+
+        :ref:`postgresql_match`
+
+    """
+
+    __visit_name__ = "TSVECTOR"
+
+
+class ENUM(sqltypes.NativeForEmulated, sqltypes.Enum):
+
+    """PostgreSQL ENUM type.
+
+    This is a subclass of :class:`_types.Enum` which includes
+    support for PG's ``CREATE TYPE`` and ``DROP TYPE``.
+
+    When the builtin type :class:`_types.Enum` is used and the
+    :paramref:`.Enum.native_enum` flag is left at its default of
+    True, the PostgreSQL backend will use a :class:`_postgresql.ENUM`
+    type as the implementation, so the special create/drop rules
+    will be used.
+
+    The create/drop behavior of ENUM is necessarily intricate, due to the
+    awkward relationship the ENUM type has in relationship to the
+    parent table, in that it may be "owned" by just a single table, or
+    may be shared among many tables.
+
+    When using :class:`_types.Enum` or :class:`_postgresql.ENUM`
+    in an "inline" fashion, the ``CREATE TYPE`` and ``DROP TYPE`` is emitted
+    corresponding to when the :meth:`_schema.Table.create` and
+    :meth:`_schema.Table.drop`
+    methods are called::
+
+        table = Table('sometable', metadata,
+            Column('some_enum', ENUM('a', 'b', 'c', name='myenum'))
+        )
+
+        table.create(engine)  # will emit CREATE ENUM and CREATE TABLE
+        table.drop(engine)  # will emit DROP TABLE and DROP ENUM
+
+    To use a common enumerated type between multiple tables, the best
+    practice is to declare the :class:`_types.Enum` or
+    :class:`_postgresql.ENUM` independently, and associate it with the
+    :class:`_schema.MetaData` object itself::
+
+        my_enum = ENUM('a', 'b', 'c', name='myenum', metadata=metadata)
+
+        t1 = Table('sometable_one', metadata,
+            Column('some_enum', myenum)
+        )
+
+        t2 = Table('sometable_two', metadata,
+            Column('some_enum', myenum)
+        )
+
+    When this pattern is used, care must still be taken at the level
+    of individual table creates.  Emitting CREATE TABLE without also
+    specifying ``checkfirst=True`` will still cause issues::
+
+        t1.create(engine) # will fail: no such type 'myenum'
+
+    If we specify ``checkfirst=True``, the individual table-level create
+    operation will check for the ``ENUM`` and create if not exists::
+
+        # will check if enum exists, and emit CREATE TYPE if not
+        t1.create(engine, checkfirst=True)
+
+    When using a metadata-level ENUM type, the type will always be created
+    and dropped if either the metadata-wide create/drop is called::
+
+        metadata.create_all(engine)  # will emit CREATE TYPE
+        metadata.drop_all(engine)  # will emit DROP TYPE
+
+    The type can also be created and dropped directly::
+
+        my_enum.create(engine)
+        my_enum.drop(engine)
+
+    .. versionchanged:: 1.0.0 The PostgreSQL :class:`_postgresql.ENUM` type
+       now behaves more strictly with regards to CREATE/DROP.  A metadata-level
+       ENUM type will only be created and dropped at the metadata level,
+       not the table level, with the exception of
+       ``table.create(checkfirst=True)``.
+       The ``table.drop()`` call will now emit a DROP TYPE for a table-level
+       enumerated type.
+
+    """
+
+    native_enum = True
+
+    def __init__(self, *enums, **kw):
+        """Construct an :class:`_postgresql.ENUM`.
+
+        Arguments are the same as that of
+        :class:`_types.Enum`, but also including
+        the following parameters.
+
+        :param create_type: Defaults to True.
+         Indicates that ``CREATE TYPE`` should be
+         emitted, after optionally checking for the
+         presence of the type, when the parent
+         table is being created; and additionally
+         that ``DROP TYPE`` is called when the table
+         is dropped.    When ``False``, no check
+         will be performed and no ``CREATE TYPE``
+         or ``DROP TYPE`` is emitted, unless
+         :meth:`~.postgresql.ENUM.create`
+         or :meth:`~.postgresql.ENUM.drop`
+         are called directly.
+         Setting to ``False`` is helpful
+         when invoking a creation scheme to a SQL file
+         without access to the actual database -
+         the :meth:`~.postgresql.ENUM.create` and
+         :meth:`~.postgresql.ENUM.drop` methods can
+         be used to emit SQL to a target bind.
+
+        """
+        native_enum = kw.pop("native_enum", None)
+        if native_enum is False:
+            util.warn(
+                "the native_enum flag does not apply to the "
+                "sqlalchemy.dialects.postgresql.ENUM datatype; this type "
+                "always refers to ENUM.   Use sqlalchemy.types.Enum for "
+                "non-native enum."
+            )
+        self.create_type = kw.pop("create_type", True)
+        super(ENUM, self).__init__(*enums, **kw)
+
+    @classmethod
+    def adapt_emulated_to_native(cls, impl, **kw):
+        """Produce a PostgreSQL native :class:`_postgresql.ENUM` from plain
+        :class:`.Enum`.
+
+        """
+        kw.setdefault("validate_strings", impl.validate_strings)
+        kw.setdefault("name", impl.name)
+        kw.setdefault("schema", impl.schema)
+        kw.setdefault("inherit_schema", impl.inherit_schema)
+        kw.setdefault("metadata", impl.metadata)
+        kw.setdefault("_create_events", False)
+        kw.setdefault("values_callable", impl.values_callable)
+        kw.setdefault("omit_aliases", impl._omit_aliases)
+        return cls(**kw)
+
+    def create(self, bind=None, checkfirst=True):
+        """Emit ``CREATE TYPE`` for this
+        :class:`_postgresql.ENUM`.
+
+        If the underlying dialect does not support
+        PostgreSQL CREATE TYPE, no action is taken.
+
+        :param bind: a connectable :class:`_engine.Engine`,
+         :class:`_engine.Connection`, or similar object to emit
+         SQL.
+        :param checkfirst: if ``True``, a query against
+         the PG catalog will be first performed to see
+         if the type does not exist already before
+         creating.
+
+        """
+        if not bind.dialect.supports_native_enum:
+            return
+
+        bind._run_ddl_visitor(self.EnumGenerator, self, checkfirst=checkfirst)
+
+    def drop(self, bind=None, checkfirst=True):
+        """Emit ``DROP TYPE`` for this
+        :class:`_postgresql.ENUM`.
+
+        If the underlying dialect does not support
+        PostgreSQL DROP TYPE, no action is taken.
+
+        :param bind: a connectable :class:`_engine.Engine`,
+         :class:`_engine.Connection`, or similar object to emit
+         SQL.
+        :param checkfirst: if ``True``, a query against
+         the PG catalog will be first performed to see
+         if the type actually exists before dropping.
+
+        """
+        if not bind.dialect.supports_native_enum:
+            return
+
+        bind._run_ddl_visitor(self.EnumDropper, self, checkfirst=checkfirst)
+
+    class EnumGenerator(DDLBase):
+        def __init__(self, dialect, connection, checkfirst=False, **kwargs):
+            super(ENUM.EnumGenerator, self).__init__(connection, **kwargs)
+            self.checkfirst = checkfirst
+
+        def _can_create_enum(self, enum):
+            if not self.checkfirst:
+                return True
+
+            effective_schema = self.connection.schema_for_object(enum)
+
+            return not self.connection.dialect.has_type(
+                self.connection, enum.name, schema=effective_schema
+            )
+
+        def visit_enum(self, enum):
+            if not self._can_create_enum(enum):
+                return
+
+            self.connection.execute(CreateEnumType(enum))
+
+    class EnumDropper(DDLBase):
+        def __init__(self, dialect, connection, checkfirst=False, **kwargs):
+            super(ENUM.EnumDropper, self).__init__(connection, **kwargs)
+            self.checkfirst = checkfirst
+
+        def _can_drop_enum(self, enum):
+            if not self.checkfirst:
+                return True
+
+            effective_schema = self.connection.schema_for_object(enum)
+
+            return self.connection.dialect.has_type(
+                self.connection, enum.name, schema=effective_schema
+            )
+
+        def visit_enum(self, enum):
+            if not self._can_drop_enum(enum):
+                return
+
+            self.connection.execute(DropEnumType(enum))
+
+    def _check_for_name_in_memos(self, checkfirst, kw):
+        """Look in the 'ddl runner' for 'memos', then
+        note our name in that collection.
+
+        This to ensure a particular named enum is operated
+        upon only once within any kind of create/drop
+        sequence without relying upon "checkfirst".
+
+        """
+        if not self.create_type:
+            return True
+        if "_ddl_runner" in kw:
+            ddl_runner = kw["_ddl_runner"]
+            if "_pg_enums" in ddl_runner.memo:
+                pg_enums = ddl_runner.memo["_pg_enums"]
+            else:
+                pg_enums = ddl_runner.memo["_pg_enums"] = set()
+            present = (self.schema, self.name) in pg_enums
+            pg_enums.add((self.schema, self.name))
+            return present
+        else:
+            return False
+
+    def _on_table_create(self, target, bind, checkfirst=False, **kw):
+        if (
+            checkfirst
+            or (
+                not self.metadata
+                and not kw.get("_is_metadata_operation", False)
+            )
+        ) and not self._check_for_name_in_memos(checkfirst, kw):
+            self.create(bind=bind, checkfirst=checkfirst)
+
+    def _on_table_drop(self, target, bind, checkfirst=False, **kw):
+        if (
+            not self.metadata
+            and not kw.get("_is_metadata_operation", False)
+            and not self._check_for_name_in_memos(checkfirst, kw)
+        ):
+            self.drop(bind=bind, checkfirst=checkfirst)
+
+    def _on_metadata_create(self, target, bind, checkfirst=False, **kw):
+        if not self._check_for_name_in_memos(checkfirst, kw):
+            self.create(bind=bind, checkfirst=checkfirst)
+
+    def _on_metadata_drop(self, target, bind, checkfirst=False, **kw):
+        if not self._check_for_name_in_memos(checkfirst, kw):
+            self.drop(bind=bind, checkfirst=checkfirst)
+
+
+class _ColonCast(elements.Cast):
+    __visit_name__ = "colon_cast"
+
+    def __init__(self, expression, type_):
+        self.type = type_
+        self.clause = expression
+        self.typeclause = elements.TypeClause(type_)
+
+
+colspecs = {
+    sqltypes.ARRAY: _array.ARRAY,
+    sqltypes.Interval: INTERVAL,
+    sqltypes.Enum: ENUM,
+    sqltypes.JSON.JSONPathType: _json.JSONPathType,
+    sqltypes.JSON: _json.JSON,
+}
+
+ischema_names = {
+    "_array": _array.ARRAY,
+    "hstore": _hstore.HSTORE,
+    "json": _json.JSON,
+    "jsonb": _json.JSONB,
+    "int4range": _ranges.INT4RANGE,
+    "int8range": _ranges.INT8RANGE,
+    "numrange": _ranges.NUMRANGE,
+    "daterange": _ranges.DATERANGE,
+    "tsrange": _ranges.TSRANGE,
+    "tstzrange": _ranges.TSTZRANGE,
+    "integer": INTEGER,
+    "bigint": BIGINT,
+    "smallint": SMALLINT,
+    "character varying": VARCHAR,
+    "character": CHAR,
+    '"char"': sqltypes.String,
+    "name": sqltypes.String,
+    "text": TEXT,
+    "numeric": NUMERIC,
+    "float": FLOAT,
+    "real": REAL,
+    "inet": INET,
+    "cidr": CIDR,
+    "uuid": UUID,
+    "bit": BIT,
+    "bit varying": BIT,
+    "macaddr": MACADDR,
+    "money": MONEY,
+    "oid": OID,
+    "regclass": REGCLASS,
+    "double precision": DOUBLE_PRECISION,
+    "timestamp": TIMESTAMP,
+    "timestamp with time zone": TIMESTAMP,
+    "timestamp without time zone": TIMESTAMP,
+    "time with time zone": TIME,
+    "time without time zone": TIME,
+    "date": DATE,
+    "time": TIME,
+    "bytea": BYTEA,
+    "boolean": BOOLEAN,
+    "interval": INTERVAL,
+    "tsvector": TSVECTOR,
+}
+
+
+class PGCompiler(compiler.SQLCompiler):
+    def visit_colon_cast(self, element, **kw):
+        return "%s::%s" % (
+            element.clause._compiler_dispatch(self, **kw),
+            element.typeclause._compiler_dispatch(self, **kw),
+        )
+
+    def visit_array(self, element, **kw):
+        return "ARRAY[%s]" % self.visit_clauselist(element, **kw)
+
+    def visit_slice(self, element, **kw):
+        return "%s:%s" % (
+            self.process(element.start, **kw),
+            self.process(element.stop, **kw),
+        )
+
+    def visit_json_getitem_op_binary(
+        self, binary, operator, _cast_applied=False, **kw
+    ):
+        if (
+            not _cast_applied
+            and binary.type._type_affinity is not sqltypes.JSON
+        ):
+            kw["_cast_applied"] = True
+            return self.process(sql.cast(binary, binary.type), **kw)
+
+        kw["eager_grouping"] = True
+
+        return self._generate_generic_binary(
+            binary, " -> " if not _cast_applied else " ->> ", **kw
+        )
+
+    def visit_json_path_getitem_op_binary(
+        self, binary, operator, _cast_applied=False, **kw
+    ):
+        if (
+            not _cast_applied
+            and binary.type._type_affinity is not sqltypes.JSON
+        ):
+            kw["_cast_applied"] = True
+            return self.process(sql.cast(binary, binary.type), **kw)
+
+        kw["eager_grouping"] = True
+        return self._generate_generic_binary(
+            binary, " #> " if not _cast_applied else " #>> ", **kw
+        )
+
+    def visit_getitem_binary(self, binary, operator, **kw):
+        return "%s[%s]" % (
+            self.process(binary.left, **kw),
+            self.process(binary.right, **kw),
+        )
+
+    def visit_aggregate_order_by(self, element, **kw):
+        return "%s ORDER BY %s" % (
+            self.process(element.target, **kw),
+            self.process(element.order_by, **kw),
+        )
+
+    def visit_match_op_binary(self, binary, operator, **kw):
+        if "postgresql_regconfig" in binary.modifiers:
+            regconfig = self.render_literal_value(
+                binary.modifiers["postgresql_regconfig"], sqltypes.STRINGTYPE
+            )
+            if regconfig:
+                return "%s @@ to_tsquery(%s, %s)" % (
+                    self.process(binary.left, **kw),
+                    regconfig,
+                    self.process(binary.right, **kw),
+                )
+        return "%s @@ to_tsquery(%s)" % (
+            self.process(binary.left, **kw),
+            self.process(binary.right, **kw),
+        )
+
+    def visit_ilike_op_binary(self, binary, operator, **kw):
+        escape = binary.modifiers.get("escape", None)
+
+        return "%s ILIKE %s" % (
+            self.process(binary.left, **kw),
+            self.process(binary.right, **kw),
+        ) + (
+            " ESCAPE " + self.render_literal_value(escape, sqltypes.STRINGTYPE)
+            if escape
+            else ""
+        )
+
+    def visit_not_ilike_op_binary(self, binary, operator, **kw):
+        escape = binary.modifiers.get("escape", None)
+        return "%s NOT ILIKE %s" % (
+            self.process(binary.left, **kw),
+            self.process(binary.right, **kw),
+        ) + (
+            " ESCAPE " + self.render_literal_value(escape, sqltypes.STRINGTYPE)
+            if escape
+            else ""
+        )
+
+    def _regexp_match(self, base_op, binary, operator, kw):
+        flags = binary.modifiers["flags"]
+        if flags is None:
+            return self._generate_generic_binary(
+                binary, " %s " % base_op, **kw
+            )
+        if isinstance(flags, elements.BindParameter) and flags.value == "i":
+            return self._generate_generic_binary(
+                binary, " %s* " % base_op, **kw
+            )
+        flags = self.process(flags, **kw)
+        string = self.process(binary.left, **kw)
+        pattern = self.process(binary.right, **kw)
+        return "%s %s CONCAT('(?', %s, ')', %s)" % (
+            string,
+            base_op,
+            flags,
+            pattern,
+        )
+
+    def visit_regexp_match_op_binary(self, binary, operator, **kw):
+        return self._regexp_match("~", binary, operator, kw)
+
+    def visit_not_regexp_match_op_binary(self, binary, operator, **kw):
+        return self._regexp_match("!~", binary, operator, kw)
+
+    def visit_regexp_replace_op_binary(self, binary, operator, **kw):
+        string = self.process(binary.left, **kw)
+        pattern = self.process(binary.right, **kw)
+        flags = binary.modifiers["flags"]
+        if flags is not None:
+            flags = self.process(flags, **kw)
+        replacement = self.process(binary.modifiers["replacement"], **kw)
+        if flags is None:
+            return "REGEXP_REPLACE(%s, %s, %s)" % (
+                string,
+                pattern,
+                replacement,
+            )
+        else:
+            return "REGEXP_REPLACE(%s, %s, %s, %s)" % (
+                string,
+                pattern,
+                replacement,
+                flags,
+            )
+
+    def visit_empty_set_expr(self, element_types):
+        # cast the empty set to the type we are comparing against.  if
+        # we are comparing against the null type, pick an arbitrary
+        # datatype for the empty set
+        return "SELECT %s WHERE 1!=1" % (
+            ", ".join(
+                "CAST(NULL AS %s)"
+                % self.dialect.type_compiler.process(
+                    INTEGER() if type_._isnull else type_
+                )
+                for type_ in element_types or [INTEGER()]
+            ),
+        )
+
+    def render_literal_value(self, value, type_):
+        value = super(PGCompiler, self).render_literal_value(value, type_)
+
+        if self.dialect._backslash_escapes:
+            value = value.replace("\\", "\\\\")
+        return value
+
+    def visit_sequence(self, seq, **kw):
+        return "nextval('%s')" % self.preparer.format_sequence(seq)
+
+    def limit_clause(self, select, **kw):
+        text = ""
+        if select._limit_clause is not None:
+            text += " \n LIMIT " + self.process(select._limit_clause, **kw)
+        if select._offset_clause is not None:
+            if select._limit_clause is None:
+                text += "\n LIMIT ALL"
+            text += " OFFSET " + self.process(select._offset_clause, **kw)
+        return text
+
+    def format_from_hint_text(self, sqltext, table, hint, iscrud):
+        if hint.upper() != "ONLY":
+            raise exc.CompileError("Unrecognized hint: %r" % hint)
+        return "ONLY " + sqltext
+
+    def get_select_precolumns(self, select, **kw):
+        # Do not call super().get_select_precolumns because
+        # it will warn/raise when distinct on is present
+        if select._distinct or select._distinct_on:
+            if select._distinct_on:
+                return (
+                    "DISTINCT ON ("
+                    + ", ".join(
+                        [
+                            self.process(col, **kw)
+                            for col in select._distinct_on
+                        ]
+                    )
+                    + ") "
+                )
+            else:
+                return "DISTINCT "
+        else:
+            return ""
+
+    def for_update_clause(self, select, **kw):
+
+        if select._for_update_arg.read:
+            if select._for_update_arg.key_share:
+                tmp = " FOR KEY SHARE"
+            else:
+                tmp = " FOR SHARE"
+        elif select._for_update_arg.key_share:
+            tmp = " FOR NO KEY UPDATE"
+        else:
+            tmp = " FOR UPDATE"
+
+        if select._for_update_arg.of:
+
+            tables = util.OrderedSet()
+            for c in select._for_update_arg.of:
+                tables.update(sql_util.surface_selectables_only(c))
+
+            tmp += " OF " + ", ".join(
+                self.process(table, ashint=True, use_schema=False, **kw)
+                for table in tables
+            )
+
+        if select._for_update_arg.nowait:
+            tmp += " NOWAIT"
+        if select._for_update_arg.skip_locked:
+            tmp += " SKIP LOCKED"
+
+        return tmp
+
+    def returning_clause(self, stmt, returning_cols):
+
+        columns = [
+            self._label_returning_column(stmt, c)
+            for c in expression._select_iterables(returning_cols)
+        ]
+
+        return "RETURNING " + ", ".join(columns)
+
+    def visit_substring_func(self, func, **kw):
+        s = self.process(func.clauses.clauses[0], **kw)
+        start = self.process(func.clauses.clauses[1], **kw)
+        if len(func.clauses.clauses) > 2:
+            length = self.process(func.clauses.clauses[2], **kw)
+            return "SUBSTRING(%s FROM %s FOR %s)" % (s, start, length)
+        else:
+            return "SUBSTRING(%s FROM %s)" % (s, start)
+
+    def _on_conflict_target(self, clause, **kw):
+
+        if clause.constraint_target is not None:
+            # target may be a name of an Index, UniqueConstraint or
+            # ExcludeConstraint.  While there is a separate
+            # "max_identifier_length" for indexes, PostgreSQL uses the same
+            # length for all objects so we can use
+            # truncate_and_render_constraint_name
+            target_text = (
+                "ON CONSTRAINT %s"
+                % self.preparer.truncate_and_render_constraint_name(
+                    clause.constraint_target
+                )
+            )
+        elif clause.inferred_target_elements is not None:
+            target_text = "(%s)" % ", ".join(
+                (
+                    self.preparer.quote(c)
+                    if isinstance(c, util.string_types)
+                    else self.process(c, include_table=False, use_schema=False)
+                )
+                for c in clause.inferred_target_elements
+            )
+            if clause.inferred_target_whereclause is not None:
+                target_text += " WHERE %s" % self.process(
+                    clause.inferred_target_whereclause,
+                    include_table=False,
+                    use_schema=False,
+                )
+        else:
+            target_text = ""
+
+        return target_text
+
+    @util.memoized_property
+    def _is_safe_for_fast_insert_values_helper(self):
+        # don't allow fast executemany if _post_values_clause is
+        # present and is not an OnConflictDoNothing. what this means
+        # concretely is that the
+        # "fast insert executemany helper" won't be used, in other
+        # words we won't convert "executemany()" of many parameter
+        # sets into a single INSERT with many elements in VALUES.
+        # We can't apply that optimization safely if for example the
+        # statement includes a clause like "ON CONFLICT DO UPDATE"
+
+        return self.insert_single_values_expr is not None and (
+            self.statement._post_values_clause is None
+            or isinstance(
+                self.statement._post_values_clause, dml.OnConflictDoNothing
+            )
+        )
+
+    def visit_on_conflict_do_nothing(self, on_conflict, **kw):
+
+        target_text = self._on_conflict_target(on_conflict, **kw)
+
+        if target_text:
+            return "ON CONFLICT %s DO NOTHING" % target_text
+        else:
+            return "ON CONFLICT DO NOTHING"
+
+    def visit_on_conflict_do_update(self, on_conflict, **kw):
+
+        clause = on_conflict
+
+        target_text = self._on_conflict_target(on_conflict, **kw)
+
+        action_set_ops = []
+
+        set_parameters = dict(clause.update_values_to_set)
+        # create a list of column assignment clauses as tuples
+
+        insert_statement = self.stack[-1]["selectable"]
+        cols = insert_statement.table.c
+        for c in cols:
+            col_key = c.key
+
+            if col_key in set_parameters:
+                value = set_parameters.pop(col_key)
+            elif c in set_parameters:
+                value = set_parameters.pop(c)
+            else:
+                continue
+
+            if coercions._is_literal(value):
+                value = elements.BindParameter(None, value, type_=c.type)
+
+            else:
+                if (
+                    isinstance(value, elements.BindParameter)
+                    and value.type._isnull
+                ):
+                    value = value._clone()
+                    value.type = c.type
+            value_text = self.process(value.self_group(), use_schema=False)
+
+            key_text = self.preparer.quote(c.name)
+            action_set_ops.append("%s = %s" % (key_text, value_text))
+
+        # check for names that don't match columns
+        if set_parameters:
+            util.warn(
+                "Additional column names not matching "
+                "any column keys in table '%s': %s"
+                % (
+                    self.current_executable.table.name,
+                    (", ".join("'%s'" % c for c in set_parameters)),
+                )
+            )
+            for k, v in set_parameters.items():
+                key_text = (
+                    self.preparer.quote(k)
+                    if isinstance(k, util.string_types)
+                    else self.process(k, use_schema=False)
+                )
+                value_text = self.process(
+                    coercions.expect(roles.ExpressionElementRole, v),
+                    use_schema=False,
+                )
+                action_set_ops.append("%s = %s" % (key_text, value_text))
+
+        action_text = ", ".join(action_set_ops)
+        if clause.update_whereclause is not None:
+            action_text += " WHERE %s" % self.process(
+                clause.update_whereclause, include_table=True, use_schema=False
+            )
+
+        return "ON CONFLICT %s DO UPDATE SET %s" % (target_text, action_text)
+
+    def update_from_clause(
+        self, update_stmt, from_table, extra_froms, from_hints, **kw
+    ):
+        kw["asfrom"] = True
+        return "FROM " + ", ".join(
+            t._compiler_dispatch(self, fromhints=from_hints, **kw)
+            for t in extra_froms
+        )
+
+    def delete_extra_from_clause(
+        self, delete_stmt, from_table, extra_froms, from_hints, **kw
+    ):
+        """Render the DELETE .. USING clause specific to PostgreSQL."""
+        kw["asfrom"] = True
+        return "USING " + ", ".join(
+            t._compiler_dispatch(self, fromhints=from_hints, **kw)
+            for t in extra_froms
+        )
+
+    def fetch_clause(self, select, **kw):
+        # pg requires parens for non literal clauses. It's also required for
+        # bind parameters if a ::type casts is used by the driver (asyncpg),
+        # so it's easiest to just always add it
+        text = ""
+        if select._offset_clause is not None:
+            text += "\n OFFSET (%s) ROWS" % self.process(
+                select._offset_clause, **kw
+            )
+        if select._fetch_clause is not None:
+            text += "\n FETCH FIRST (%s)%s ROWS %s" % (
+                self.process(select._fetch_clause, **kw),
+                " PERCENT" if select._fetch_clause_options["percent"] else "",
+                "WITH TIES"
+                if select._fetch_clause_options["with_ties"]
+                else "ONLY",
+            )
+        return text
+
+
+class PGDDLCompiler(compiler.DDLCompiler):
+    def get_column_specification(self, column, **kwargs):
+
+        colspec = self.preparer.format_column(column)
+        impl_type = column.type.dialect_impl(self.dialect)
+        if isinstance(impl_type, sqltypes.TypeDecorator):
+            impl_type = impl_type.impl
+
+        has_identity = (
+            column.identity is not None
+            and self.dialect.supports_identity_columns
+        )
+
+        if (
+            column.primary_key
+            and column is column.table._autoincrement_column
+            and (
+                self.dialect.supports_smallserial
+                or not isinstance(impl_type, sqltypes.SmallInteger)
+            )
+            and not has_identity
+            and (
+                column.default is None
+                or (
+                    isinstance(column.default, schema.Sequence)
+                    and column.default.optional
+                )
+            )
+        ):
+            if isinstance(impl_type, sqltypes.BigInteger):
+                colspec += " BIGSERIAL"
+            elif isinstance(impl_type, sqltypes.SmallInteger):
+                colspec += " SMALLSERIAL"
+            else:
+                colspec += " SERIAL"
+        else:
+            colspec += " " + self.dialect.type_compiler.process(
+                column.type,
+                type_expression=column,
+                identifier_preparer=self.preparer,
+            )
+            default = self.get_column_default_string(column)
+            if default is not None:
+                colspec += " DEFAULT " + default
+
+        if column.computed is not None:
+            colspec += " " + self.process(column.computed)
+        if has_identity:
+            colspec += " " + self.process(column.identity)
+
+        if not column.nullable and not has_identity:
+            colspec += " NOT NULL"
+        elif column.nullable and has_identity:
+            colspec += " NULL"
+        return colspec
+
+    def _define_constraint_validity(self, constraint):
+        not_valid = constraint.dialect_options["postgresql"]["not_valid"]
+        return " NOT VALID" if not_valid else ""
+
+    def visit_check_constraint(self, constraint):
+        if constraint._type_bound:
+            typ = list(constraint.columns)[0].type
+            if (
+                isinstance(typ, sqltypes.ARRAY)
+                and isinstance(typ.item_type, sqltypes.Enum)
+                and not typ.item_type.native_enum
+            ):
+                raise exc.CompileError(
+                    "PostgreSQL dialect cannot produce the CHECK constraint "
+                    "for ARRAY of non-native ENUM; please specify "
+                    "create_constraint=False on this Enum datatype."
+                )
+
+        text = super(PGDDLCompiler, self).visit_check_constraint(constraint)
+        text += self._define_constraint_validity(constraint)
+        return text
+
+    def visit_foreign_key_constraint(self, constraint):
+        text = super(PGDDLCompiler, self).visit_foreign_key_constraint(
+            constraint
+        )
+        text += self._define_constraint_validity(constraint)
+        return text
+
+    def visit_drop_table_comment(self, drop):
+        return "COMMENT ON TABLE %s IS NULL" % self.preparer.format_table(
+            drop.element
+        )
+
+    def visit_create_enum_type(self, create):
+        type_ = create.element
+
+        return "CREATE TYPE %s AS ENUM (%s)" % (
+            self.preparer.format_type(type_),
+            ", ".join(
+                self.sql_compiler.process(sql.literal(e), literal_binds=True)
+                for e in type_.enums
+            ),
+        )
+
+    def visit_drop_enum_type(self, drop):
+        type_ = drop.element
+
+        return "DROP TYPE %s" % (self.preparer.format_type(type_))
+
+    def visit_create_index(self, create):
+        preparer = self.preparer
+        index = create.element
+        self._verify_index_table(index)
+        text = "CREATE "
+        if index.unique:
+            text += "UNIQUE "
+        text += "INDEX "
+
+        if self.dialect._supports_create_index_concurrently:
+            concurrently = index.dialect_options["postgresql"]["concurrently"]
+            if concurrently:
+                text += "CONCURRENTLY "
+
+        if create.if_not_exists:
+            text += "IF NOT EXISTS "
+
+        text += "%s ON %s " % (
+            self._prepared_index_name(index, include_schema=False),
+            preparer.format_table(index.table),
+        )
+
+        using = index.dialect_options["postgresql"]["using"]
+        if using:
+            text += (
+                "USING %s "
+                % self.preparer.validate_sql_phrase(using, IDX_USING).lower()
+            )
+
+        ops = index.dialect_options["postgresql"]["ops"]
+        text += "(%s)" % (
+            ", ".join(
+                [
+                    self.sql_compiler.process(
+                        expr.self_group()
+                        if not isinstance(expr, expression.ColumnClause)
+                        else expr,
+                        include_table=False,
+                        literal_binds=True,
+                    )
+                    + (
+                        (" " + ops[expr.key])
+                        if hasattr(expr, "key") and expr.key in ops
+                        else ""
+                    )
+                    for expr in index.expressions
+                ]
+            )
+        )
+
+        includeclause = index.dialect_options["postgresql"]["include"]
+        if includeclause:
+            inclusions = [
+                index.table.c[col]
+                if isinstance(col, util.string_types)
+                else col
+                for col in includeclause
+            ]
+            text += " INCLUDE (%s)" % ", ".join(
+                [preparer.quote(c.name) for c in inclusions]
+            )
+
+        withclause = index.dialect_options["postgresql"]["with"]
+        if withclause:
+            text += " WITH (%s)" % (
+                ", ".join(
+                    [
+                        "%s = %s" % storage_parameter
+                        for storage_parameter in withclause.items()
+                    ]
+                )
+            )
+
+        tablespace_name = index.dialect_options["postgresql"]["tablespace"]
+        if tablespace_name:
+            text += " TABLESPACE %s" % preparer.quote(tablespace_name)
+
+        whereclause = index.dialect_options["postgresql"]["where"]
+        if whereclause is not None:
+            whereclause = coercions.expect(
+                roles.DDLExpressionRole, whereclause
+            )
+
+            where_compiled = self.sql_compiler.process(
+                whereclause, include_table=False, literal_binds=True
+            )
+            text += " WHERE " + where_compiled
+
+        return text
+
+    def visit_drop_index(self, drop):
+        index = drop.element
+
+        text = "\nDROP INDEX "
+
+        if self.dialect._supports_drop_index_concurrently:
+            concurrently = index.dialect_options["postgresql"]["concurrently"]
+            if concurrently:
+                text += "CONCURRENTLY "
+
+        if drop.if_exists:
+            text += "IF EXISTS "
+
+        text += self._prepared_index_name(index, include_schema=True)
+        return text
+
+    def visit_exclude_constraint(self, constraint, **kw):
+        text = ""
+        if constraint.name is not None:
+            text += "CONSTRAINT %s " % self.preparer.format_constraint(
+                constraint
+            )
+        elements = []
+        for expr, name, op in constraint._render_exprs:
+            kw["include_table"] = False
+            exclude_element = self.sql_compiler.process(expr, **kw) + (
+                (" " + constraint.ops[expr.key])
+                if hasattr(expr, "key") and expr.key in constraint.ops
+                else ""
+            )
+
+            elements.append("%s WITH %s" % (exclude_element, op))
+        text += "EXCLUDE USING %s (%s)" % (
+            self.preparer.validate_sql_phrase(
+                constraint.using, IDX_USING
+            ).lower(),
+            ", ".join(elements),
+        )
+        if constraint.where is not None:
+            text += " WHERE (%s)" % self.sql_compiler.process(
+                constraint.where, literal_binds=True
+            )
+        text += self.define_constraint_deferrability(constraint)
+        return text
+
+    def post_create_table(self, table):
+        table_opts = []
+        pg_opts = table.dialect_options["postgresql"]
+
+        inherits = pg_opts.get("inherits")
+        if inherits is not None:
+            if not isinstance(inherits, (list, tuple)):
+                inherits = (inherits,)
+            table_opts.append(
+                "\n INHERITS ( "
+                + ", ".join(self.preparer.quote(name) for name in inherits)
+                + " )"
+            )
+
+        if pg_opts["partition_by"]:
+            table_opts.append("\n PARTITION BY %s" % pg_opts["partition_by"])
+
+        if pg_opts["with_oids"] is True:
+            table_opts.append("\n WITH OIDS")
+        elif pg_opts["with_oids"] is False:
+            table_opts.append("\n WITHOUT OIDS")
+
+        if pg_opts["on_commit"]:
+            on_commit_options = pg_opts["on_commit"].replace("_", " ").upper()
+            table_opts.append("\n ON COMMIT %s" % on_commit_options)
+
+        if pg_opts["tablespace"]:
+            tablespace_name = pg_opts["tablespace"]
+            table_opts.append(
+                "\n TABLESPACE %s" % self.preparer.quote(tablespace_name)
+            )
+
+        return "".join(table_opts)
+
+    def visit_computed_column(self, generated):
+        if generated.persisted is False:
+            raise exc.CompileError(
+                "PostrgreSQL computed columns do not support 'virtual' "
+                "persistence; set the 'persisted' flag to None or True for "
+                "PostgreSQL support."
+            )
+
+        return "GENERATED ALWAYS AS (%s) STORED" % self.sql_compiler.process(
+            generated.sqltext, include_table=False, literal_binds=True
+        )
+
+    def visit_create_sequence(self, create, **kw):
+        prefix = None
+        if create.element.data_type is not None:
+            prefix = " AS %s" % self.type_compiler.process(
+                create.element.data_type
+            )
+
+        return super(PGDDLCompiler, self).visit_create_sequence(
+            create, prefix=prefix, **kw
+        )
+
+
+class PGTypeCompiler(compiler.GenericTypeCompiler):
+    def visit_TSVECTOR(self, type_, **kw):
+        return "TSVECTOR"
+
+    def visit_INET(self, type_, **kw):
+        return "INET"
+
+    def visit_CIDR(self, type_, **kw):
+        return "CIDR"
+
+    def visit_MACADDR(self, type_, **kw):
+        return "MACADDR"
+
+    def visit_MONEY(self, type_, **kw):
+        return "MONEY"
+
+    def visit_OID(self, type_, **kw):
+        return "OID"
+
+    def visit_REGCLASS(self, type_, **kw):
+        return "REGCLASS"
+
+    def visit_FLOAT(self, type_, **kw):
+        if not type_.precision:
+            return "FLOAT"
+        else:
+            return "FLOAT(%(precision)s)" % {"precision": type_.precision}
+
+    def visit_DOUBLE_PRECISION(self, type_, **kw):
+        return "DOUBLE PRECISION"
+
+    def visit_BIGINT(self, type_, **kw):
+        return "BIGINT"
+
+    def visit_HSTORE(self, type_, **kw):
+        return "HSTORE"
+
+    def visit_JSON(self, type_, **kw):
+        return "JSON"
+
+    def visit_JSONB(self, type_, **kw):
+        return "JSONB"
+
+    def visit_INT4RANGE(self, type_, **kw):
+        return "INT4RANGE"
+
+    def visit_INT8RANGE(self, type_, **kw):
+        return "INT8RANGE"
+
+    def visit_NUMRANGE(self, type_, **kw):
+        return "NUMRANGE"
+
+    def visit_DATERANGE(self, type_, **kw):
+        return "DATERANGE"
+
+    def visit_TSRANGE(self, type_, **kw):
+        return "TSRANGE"
+
+    def visit_TSTZRANGE(self, type_, **kw):
+        return "TSTZRANGE"
+
+    def visit_datetime(self, type_, **kw):
+        return self.visit_TIMESTAMP(type_, **kw)
+
+    def visit_enum(self, type_, **kw):
+        if not type_.native_enum or not self.dialect.supports_native_enum:
+            return super(PGTypeCompiler, self).visit_enum(type_, **kw)
+        else:
+            return self.visit_ENUM(type_, **kw)
+
+    def visit_ENUM(self, type_, identifier_preparer=None, **kw):
+        if identifier_preparer is None:
+            identifier_preparer = self.dialect.identifier_preparer
+        return identifier_preparer.format_type(type_)
+
+    def visit_TIMESTAMP(self, type_, **kw):
+        return "TIMESTAMP%s %s" % (
+            "(%d)" % type_.precision
+            if getattr(type_, "precision", None) is not None
+            else "",
+            (type_.timezone and "WITH" or "WITHOUT") + " TIME ZONE",
+        )
+
+    def visit_TIME(self, type_, **kw):
+        return "TIME%s %s" % (
+            "(%d)" % type_.precision
+            if getattr(type_, "precision", None) is not None
+            else "",
+            (type_.timezone and "WITH" or "WITHOUT") + " TIME ZONE",
+        )
+
+    def visit_INTERVAL(self, type_, **kw):
+        text = "INTERVAL"
+        if type_.fields is not None:
+            text += " " + type_.fields
+        if type_.precision is not None:
+            text += " (%d)" % type_.precision
+        return text
+
+    def visit_BIT(self, type_, **kw):
+        if type_.varying:
+            compiled = "BIT VARYING"
+            if type_.length is not None:
+                compiled += "(%d)" % type_.length
+        else:
+            compiled = "BIT(%d)" % type_.length
+        return compiled
+
+    def visit_UUID(self, type_, **kw):
+        return "UUID"
+
+    def visit_large_binary(self, type_, **kw):
+        return self.visit_BYTEA(type_, **kw)
+
+    def visit_BYTEA(self, type_, **kw):
+        return "BYTEA"
+
+    def visit_ARRAY(self, type_, **kw):
+
+        inner = self.process(type_.item_type, **kw)
+        return re.sub(
+            r"((?: COLLATE.*)?)$",
+            (
+                r"%s\1"
+                % (
+                    "[]"
+                    * (type_.dimensions if type_.dimensions is not None else 1)
+                )
+            ),
+            inner,
+            count=1,
+        )
+
+
+class PGIdentifierPreparer(compiler.IdentifierPreparer):
+
+    reserved_words = RESERVED_WORDS
+
+    def _unquote_identifier(self, value):
+        if value[0] == self.initial_quote:
+            value = value[1:-1].replace(
+                self.escape_to_quote, self.escape_quote
+            )
+        return value
+
+    def format_type(self, type_, use_schema=True):
+        if not type_.name:
+            raise exc.CompileError("PostgreSQL ENUM type requires a name.")
+
+        name = self.quote(type_.name)
+        effective_schema = self.schema_for_object(type_)
+
+        if (
+            not self.omit_schema
+            and use_schema
+            and effective_schema is not None
+        ):
+            name = self.quote_schema(effective_schema) + "." + name
+        return name
+
+
+class PGInspector(reflection.Inspector):
+    def get_table_oid(self, table_name, schema=None):
+        """Return the OID for the given table name."""
+
+        with self._operation_context() as conn:
+            return self.dialect.get_table_oid(
+                conn, table_name, schema, info_cache=self.info_cache
+            )
+
+    def get_enums(self, schema=None):
+        """Return a list of ENUM objects.
+
+        Each member is a dictionary containing these fields:
+
+            * name - name of the enum
+            * schema - the schema name for the enum.
+            * visible - boolean, whether or not this enum is visible
+              in the default search path.
+            * labels - a list of string labels that apply to the enum.
+
+        :param schema: schema name.  If None, the default schema
+         (typically 'public') is used.  May also be set to '*' to
+         indicate load enums for all schemas.
+
+        .. versionadded:: 1.0.0
+
+        """
+        schema = schema or self.default_schema_name
+        with self._operation_context() as conn:
+            return self.dialect._load_enums(conn, schema)
+
+    def get_foreign_table_names(self, schema=None):
+        """Return a list of FOREIGN TABLE names.
+
+        Behavior is similar to that of
+        :meth:`_reflection.Inspector.get_table_names`,
+        except that the list is limited to those tables that report a
+        ``relkind`` value of ``f``.
+
+        .. versionadded:: 1.0.0
+
+        """
+        schema = schema or self.default_schema_name
+        with self._operation_context() as conn:
+            return self.dialect._get_foreign_table_names(conn, schema)
+
+    def get_view_names(self, schema=None, include=("plain", "materialized")):
+        """Return all view names in `schema`.
+
+        :param schema: Optional, retrieve names from a non-default schema.
+         For special quoting, use :class:`.quoted_name`.
+
+        :param include: specify which types of views to return.  Passed
+         as a string value (for a single type) or a tuple (for any number
+         of types).  Defaults to ``('plain', 'materialized')``.
+
+         .. versionadded:: 1.1
+
+        """
+
+        with self._operation_context() as conn:
+            return self.dialect.get_view_names(
+                conn, schema, info_cache=self.info_cache, include=include
+            )
+
+
+class CreateEnumType(schema._CreateDropBase):
+    __visit_name__ = "create_enum_type"
+
+
+class DropEnumType(schema._CreateDropBase):
+    __visit_name__ = "drop_enum_type"
+
+
+class PGExecutionContext(default.DefaultExecutionContext):
+    def fire_sequence(self, seq, type_):
+        return self._execute_scalar(
+            (
+                "select nextval('%s')"
+                % self.identifier_preparer.format_sequence(seq)
+            ),
+            type_,
+        )
+
+    def get_insert_default(self, column):
+        if column.primary_key and column is column.table._autoincrement_column:
+            if column.server_default and column.server_default.has_argument:
+
+                # pre-execute passive defaults on primary key columns
+                return self._execute_scalar(
+                    "select %s" % column.server_default.arg, column.type
+                )
+
+            elif column.default is None or (
+                column.default.is_sequence and column.default.optional
+            ):
+                # execute the sequence associated with a SERIAL primary
+                # key column. for non-primary-key SERIAL, the ID just
+                # generates server side.
+
+                try:
+                    seq_name = column._postgresql_seq_name
+                except AttributeError:
+                    tab = column.table.name
+                    col = column.name
+                    tab = tab[0 : 29 + max(0, (29 - len(col)))]
+                    col = col[0 : 29 + max(0, (29 - len(tab)))]
+                    name = "%s_%s_seq" % (tab, col)
+                    column._postgresql_seq_name = seq_name = name
+
+                if column.table is not None:
+                    effective_schema = self.connection.schema_for_object(
+                        column.table
+                    )
+                else:
+                    effective_schema = None
+
+                if effective_schema is not None:
+                    exc = 'select nextval(\'"%s"."%s"\')' % (
+                        effective_schema,
+                        seq_name,
+                    )
+                else:
+                    exc = "select nextval('\"%s\"')" % (seq_name,)
+
+                return self._execute_scalar(exc, column.type)
+
+        return super(PGExecutionContext, self).get_insert_default(column)
+
+    def should_autocommit_text(self, statement):
+        return AUTOCOMMIT_REGEXP.match(statement)
+
+
+class PGReadOnlyConnectionCharacteristic(
+    characteristics.ConnectionCharacteristic
+):
+    transactional = True
+
+    def reset_characteristic(self, dialect, dbapi_conn):
+        dialect.set_readonly(dbapi_conn, False)
+
+    def set_characteristic(self, dialect, dbapi_conn, value):
+        dialect.set_readonly(dbapi_conn, value)
+
+    def get_characteristic(self, dialect, dbapi_conn):
+        return dialect.get_readonly(dbapi_conn)
+
+
+class PGDeferrableConnectionCharacteristic(
+    characteristics.ConnectionCharacteristic
+):
+    transactional = True
+
+    def reset_characteristic(self, dialect, dbapi_conn):
+        dialect.set_deferrable(dbapi_conn, False)
+
+    def set_characteristic(self, dialect, dbapi_conn, value):
+        dialect.set_deferrable(dbapi_conn, value)
+
+    def get_characteristic(self, dialect, dbapi_conn):
+        return dialect.get_deferrable(dbapi_conn)
+
+
+class PGDialect(default.DefaultDialect):
+    name = "postgresql"
+    supports_statement_cache = True
+    supports_alter = True
+    max_identifier_length = 63
+    supports_sane_rowcount = True
+
+    supports_native_enum = True
+    supports_native_boolean = True
+    supports_smallserial = True
+
+    supports_sequences = True
+    sequences_optional = True
+    preexecute_autoincrement_sequences = True
+    postfetch_lastrowid = False
+
+    supports_comments = True
+    supports_default_values = True
+
+    supports_default_metavalue = True
+
+    supports_empty_insert = False
+    supports_multivalues_insert = True
+    supports_identity_columns = True
+
+    default_paramstyle = "pyformat"
+    ischema_names = ischema_names
+    colspecs = colspecs
+
+    statement_compiler = PGCompiler
+    ddl_compiler = PGDDLCompiler
+    type_compiler = PGTypeCompiler
+    preparer = PGIdentifierPreparer
+    execution_ctx_cls = PGExecutionContext
+    inspector = PGInspector
+    isolation_level = None
+
+    implicit_returning = True
+    full_returning = True
+
+    connection_characteristics = (
+        default.DefaultDialect.connection_characteristics
+    )
+    connection_characteristics = connection_characteristics.union(
+        {
+            "postgresql_readonly": PGReadOnlyConnectionCharacteristic(),
+            "postgresql_deferrable": PGDeferrableConnectionCharacteristic(),
+        }
+    )
+
+    construct_arguments = [
+        (
+            schema.Index,
+            {
+                "using": False,
+                "include": None,
+                "where": None,
+                "ops": {},
+                "concurrently": False,
+                "with": {},
+                "tablespace": None,
+            },
+        ),
+        (
+            schema.Table,
+            {
+                "ignore_search_path": False,
+                "tablespace": None,
+                "partition_by": None,
+                "with_oids": None,
+                "on_commit": None,
+                "inherits": None,
+            },
+        ),
+        (
+            schema.CheckConstraint,
+            {
+                "not_valid": False,
+            },
+        ),
+        (
+            schema.ForeignKeyConstraint,
+            {
+                "not_valid": False,
+            },
+        ),
+    ]
+
+    reflection_options = ("postgresql_ignore_search_path",)
+
+    _backslash_escapes = True
+    _supports_create_index_concurrently = True
+    _supports_drop_index_concurrently = True
+
+    def __init__(
+        self,
+        isolation_level=None,
+        json_serializer=None,
+        json_deserializer=None,
+        **kwargs
+    ):
+        default.DefaultDialect.__init__(self, **kwargs)
+
+        # the isolation_level parameter to the PGDialect itself is legacy.
+        # still works however the execution_options method is the one that
+        # is documented.
+        self.isolation_level = isolation_level
+        self._json_deserializer = json_deserializer
+        self._json_serializer = json_serializer
+
+    def initialize(self, connection):
+        super(PGDialect, self).initialize(connection)
+
+        if self.server_version_info <= (8, 2):
+            self.full_returning = self.implicit_returning = False
+
+        self.supports_native_enum = self.server_version_info >= (8, 3)
+        if not self.supports_native_enum:
+            self.colspecs = self.colspecs.copy()
+            # pop base Enum type
+            self.colspecs.pop(sqltypes.Enum, None)
+            # psycopg2, others may have placed ENUM here as well
+            self.colspecs.pop(ENUM, None)
+
+        # https://www.postgresql.org/docs/9.3/static/release-9-2.html#AEN116689
+        self.supports_smallserial = self.server_version_info >= (9, 2)
+
+        if self.server_version_info < (8, 2):
+            self._backslash_escapes = False
+        else:
+            # ensure this query is not emitted on server version < 8.2
+            # as it will fail
+            std_string = connection.exec_driver_sql(
+                "show standard_conforming_strings"
+            ).scalar()
+            self._backslash_escapes = std_string == "off"
+
+        self._supports_create_index_concurrently = (
+            self.server_version_info >= (8, 2)
+        )
+        self._supports_drop_index_concurrently = self.server_version_info >= (
+            9,
+            2,
+        )
+        self.supports_identity_columns = self.server_version_info >= (10,)
+
+    def on_connect(self):
+        if self.isolation_level is not None:
+
+            def connect(conn):
+                self.set_isolation_level(conn, self.isolation_level)
+
+            return connect
+        else:
+            return None
+
+    _isolation_lookup = set(
+        [
+            "SERIALIZABLE",
+            "READ UNCOMMITTED",
+            "READ COMMITTED",
+            "REPEATABLE READ",
+        ]
+    )
+
+    def set_isolation_level(self, connection, level):
+        level = level.replace("_", " ")
+        if level not in self._isolation_lookup:
+            raise exc.ArgumentError(
+                "Invalid value '%s' for isolation_level. "
+                "Valid isolation levels for %s are %s"
+                % (level, self.name, ", ".join(self._isolation_lookup))
+            )
+        cursor = connection.cursor()
+        cursor.execute(
+            "SET SESSION CHARACTERISTICS AS TRANSACTION "
+            "ISOLATION LEVEL %s" % level
+        )
+        cursor.execute("COMMIT")
+        cursor.close()
+
+    def get_isolation_level(self, connection):
+        cursor = connection.cursor()
+        cursor.execute("show transaction isolation level")
+        val = cursor.fetchone()[0]
+        cursor.close()
+        return val.upper()
+
+    def set_readonly(self, connection, value):
+        raise NotImplementedError()
+
+    def get_readonly(self, connection):
+        raise NotImplementedError()
+
+    def set_deferrable(self, connection, value):
+        raise NotImplementedError()
+
+    def get_deferrable(self, connection):
+        raise NotImplementedError()
+
+    def do_begin_twophase(self, connection, xid):
+        self.do_begin(connection.connection)
+
+    def do_prepare_twophase(self, connection, xid):
+        connection.exec_driver_sql("PREPARE TRANSACTION '%s'" % xid)
+
+    def do_rollback_twophase(
+        self, connection, xid, is_prepared=True, recover=False
+    ):
+        if is_prepared:
+            if recover:
+                # FIXME: ugly hack to get out of transaction
+                # context when committing recoverable transactions
+                # Must find out a way how to make the dbapi not
+                # open a transaction.
+                connection.exec_driver_sql("ROLLBACK")
+            connection.exec_driver_sql("ROLLBACK PREPARED '%s'" % xid)
+            connection.exec_driver_sql("BEGIN")
+            self.do_rollback(connection.connection)
+        else:
+            self.do_rollback(connection.connection)
+
+    def do_commit_twophase(
+        self, connection, xid, is_prepared=True, recover=False
+    ):
+        if is_prepared:
+            if recover:
+                connection.exec_driver_sql("ROLLBACK")
+            connection.exec_driver_sql("COMMIT PREPARED '%s'" % xid)
+            connection.exec_driver_sql("BEGIN")
+            self.do_rollback(connection.connection)
+        else:
+            self.do_commit(connection.connection)
+
+    def do_recover_twophase(self, connection):
+        resultset = connection.execute(
+            sql.text("SELECT gid FROM pg_prepared_xacts")
+        )
+        return [row[0] for row in resultset]
+
+    def _get_default_schema_name(self, connection):
+        return connection.exec_driver_sql("select current_schema()").scalar()
+
+    def has_schema(self, connection, schema):
+        query = (
+            "select nspname from pg_namespace " "where lower(nspname)=:schema"
+        )
+        cursor = connection.execute(
+            sql.text(query).bindparams(
+                sql.bindparam(
+                    "schema",
+                    util.text_type(schema.lower()),
+                    type_=sqltypes.Unicode,
+                )
+            )
+        )
+
+        return bool(cursor.first())
+
+    def has_table(self, connection, table_name, schema=None):
+        self._ensure_has_table_connection(connection)
+        # seems like case gets folded in pg_class...
+        if schema is None:
+            cursor = connection.execute(
+                sql.text(
+                    "select relname from pg_class c join pg_namespace n on "
+                    "n.oid=c.relnamespace where "
+                    "pg_catalog.pg_table_is_visible(c.oid) "
+                    "and relname=:name"
+                ).bindparams(
+                    sql.bindparam(
+                        "name",
+                        util.text_type(table_name),
+                        type_=sqltypes.Unicode,
+                    )
+                )
+            )
+        else:
+            cursor = connection.execute(
+                sql.text(
+                    "select relname from pg_class c join pg_namespace n on "
+                    "n.oid=c.relnamespace where n.nspname=:schema and "
+                    "relname=:name"
+                ).bindparams(
+                    sql.bindparam(
+                        "name",
+                        util.text_type(table_name),
+                        type_=sqltypes.Unicode,
+                    ),
+                    sql.bindparam(
+                        "schema",
+                        util.text_type(schema),
+                        type_=sqltypes.Unicode,
+                    ),
+                )
+            )
+        return bool(cursor.first())
+
+    def has_sequence(self, connection, sequence_name, schema=None):
+        if schema is None:
+            schema = self.default_schema_name
+        cursor = connection.execute(
+            sql.text(
+                "SELECT relname FROM pg_class c join pg_namespace n on "
+                "n.oid=c.relnamespace where relkind='S' and "
+                "n.nspname=:schema and relname=:name"
+            ).bindparams(
+                sql.bindparam(
+                    "name",
+                    util.text_type(sequence_name),
+                    type_=sqltypes.Unicode,
+                ),
+                sql.bindparam(
+                    "schema",
+                    util.text_type(schema),
+                    type_=sqltypes.Unicode,
+                ),
+            )
+        )
+
+        return bool(cursor.first())
+
+    def has_type(self, connection, type_name, schema=None):
+        if schema is not None:
+            query = """
+            SELECT EXISTS (
+                SELECT * FROM pg_catalog.pg_type t, pg_catalog.pg_namespace n
+                WHERE t.typnamespace = n.oid
+                AND t.typname = :typname
+                AND n.nspname = :nspname
+                )
+                """
+            query = sql.text(query)
+        else:
+            query = """
+            SELECT EXISTS (
+                SELECT * FROM pg_catalog.pg_type t
+                WHERE t.typname = :typname
+                AND pg_type_is_visible(t.oid)
+                )
+                """
+            query = sql.text(query)
+        query = query.bindparams(
+            sql.bindparam(
+                "typname", util.text_type(type_name), type_=sqltypes.Unicode
+            )
+        )
+        if schema is not None:
+            query = query.bindparams(
+                sql.bindparam(
+                    "nspname", util.text_type(schema), type_=sqltypes.Unicode
+                )
+            )
+        cursor = connection.execute(query)
+        return bool(cursor.scalar())
+
+    def _get_server_version_info(self, connection):
+        v = connection.exec_driver_sql("select pg_catalog.version()").scalar()
+        m = re.match(
+            r".*(?:PostgreSQL|EnterpriseDB) "
+            r"(\d+)\.?(\d+)?(?:\.(\d+))?(?:\.\d+)?(?:devel|beta)?",
+            v,
+        )
+        if not m:
+            raise AssertionError(
+                "Could not determine version from string '%s'" % v
+            )
+        return tuple([int(x) for x in m.group(1, 2, 3) if x is not None])
+
+    @reflection.cache
+    def get_table_oid(self, connection, table_name, schema=None, **kw):
+        """Fetch the oid for schema.table_name.
+
+        Several reflection methods require the table oid.  The idea for using
+        this method is that it can be fetched one time and cached for
+        subsequent calls.
+
+        """
+        table_oid = None
+        if schema is not None:
+            schema_where_clause = "n.nspname = :schema"
+        else:
+            schema_where_clause = "pg_catalog.pg_table_is_visible(c.oid)"
+        query = (
+            """
+            SELECT c.oid
+            FROM pg_catalog.pg_class c
+            LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
+            WHERE (%s)
+            AND c.relname = :table_name AND c.relkind in
+            ('r', 'v', 'm', 'f', 'p')
+        """
+            % schema_where_clause
+        )
+        # Since we're binding to unicode, table_name and schema_name must be
+        # unicode.
+        table_name = util.text_type(table_name)
+        if schema is not None:
+            schema = util.text_type(schema)
+        s = sql.text(query).bindparams(table_name=sqltypes.Unicode)
+        s = s.columns(oid=sqltypes.Integer)
+        if schema:
+            s = s.bindparams(sql.bindparam("schema", type_=sqltypes.Unicode))
+        c = connection.execute(s, dict(table_name=table_name, schema=schema))
+        table_oid = c.scalar()
+        if table_oid is None:
+            raise exc.NoSuchTableError(table_name)
+        return table_oid
+
+    @reflection.cache
+    def get_schema_names(self, connection, **kw):
+        result = connection.execute(
+            sql.text(
+                "SELECT nspname FROM pg_namespace "
+                "WHERE nspname NOT LIKE 'pg_%' "
+                "ORDER BY nspname"
+            ).columns(nspname=sqltypes.Unicode)
+        )
+        return [name for name, in result]
+
+    @reflection.cache
+    def get_table_names(self, connection, schema=None, **kw):
+        result = connection.execute(
+            sql.text(
+                "SELECT c.relname FROM pg_class c "
+                "JOIN pg_namespace n ON n.oid = c.relnamespace "
+                "WHERE n.nspname = :schema AND c.relkind in ('r', 'p')"
+            ).columns(relname=sqltypes.Unicode),
+            dict(
+                schema=schema
+                if schema is not None
+                else self.default_schema_name
+            ),
+        )
+        return [name for name, in result]
+
+    @reflection.cache
+    def _get_foreign_table_names(self, connection, schema=None, **kw):
+        result = connection.execute(
+            sql.text(
+                "SELECT c.relname FROM pg_class c "
+                "JOIN pg_namespace n ON n.oid = c.relnamespace "
+                "WHERE n.nspname = :schema AND c.relkind = 'f'"
+            ).columns(relname=sqltypes.Unicode),
+            dict(
+                schema=schema
+                if schema is not None
+                else self.default_schema_name
+            ),
+        )
+        return [name for name, in result]
+
+    @reflection.cache
+    def get_view_names(
+        self, connection, schema=None, include=("plain", "materialized"), **kw
+    ):
+
+        include_kind = {"plain": "v", "materialized": "m"}
+        try:
+            kinds = [include_kind[i] for i in util.to_list(include)]
+        except KeyError:
+            raise ValueError(
+                "include %r unknown, needs to be a sequence containing "
+                "one or both of 'plain' and 'materialized'" % (include,)
+            )
+        if not kinds:
+            raise ValueError(
+                "empty include, needs to be a sequence containing "
+                "one or both of 'plain' and 'materialized'"
+            )
+
+        result = connection.execute(
+            sql.text(
+                "SELECT c.relname FROM pg_class c "
+                "JOIN pg_namespace n ON n.oid = c.relnamespace "
+                "WHERE n.nspname = :schema AND c.relkind IN (%s)"
+                % (", ".join("'%s'" % elem for elem in kinds))
+            ).columns(relname=sqltypes.Unicode),
+            dict(
+                schema=schema
+                if schema is not None
+                else self.default_schema_name
+            ),
+        )
+        return [name for name, in result]
+
+    @reflection.cache
+    def get_sequence_names(self, connection, schema=None, **kw):
+        if not schema:
+            schema = self.default_schema_name
+        cursor = connection.execute(
+            sql.text(
+                "SELECT relname FROM pg_class c join pg_namespace n on "
+                "n.oid=c.relnamespace where relkind='S' and "
+                "n.nspname=:schema"
+            ).bindparams(
+                sql.bindparam(
+                    "schema",
+                    util.text_type(schema),
+                    type_=sqltypes.Unicode,
+                ),
+            )
+        )
+        return [row[0] for row in cursor]
+
+    @reflection.cache
+    def get_view_definition(self, connection, view_name, schema=None, **kw):
+        view_def = connection.scalar(
+            sql.text(
+                "SELECT pg_get_viewdef(c.oid) view_def FROM pg_class c "
+                "JOIN pg_namespace n ON n.oid = c.relnamespace "
+                "WHERE n.nspname = :schema AND c.relname = :view_name "
+                "AND c.relkind IN ('v', 'm')"
+            ).columns(view_def=sqltypes.Unicode),
+            dict(
+                schema=schema
+                if schema is not None
+                else self.default_schema_name,
+                view_name=view_name,
+            ),
+        )
+        return view_def
+
+    @reflection.cache
+    def get_columns(self, connection, table_name, schema=None, **kw):
+
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        generated = (
+            "a.attgenerated as generated"
+            if self.server_version_info >= (12,)
+            else "NULL as generated"
+        )
+        if self.server_version_info >= (10,):
+            # a.attidentity != '' is required or it will reflect also
+            # serial columns as identity.
+            identity = """\
+                (SELECT json_build_object(
+                    'always', a.attidentity = 'a',
+                    'start', s.seqstart,
+                    'increment', s.seqincrement,
+                    'minvalue', s.seqmin,
+                    'maxvalue', s.seqmax,
+                    'cache', s.seqcache,
+                    'cycle', s.seqcycle)
+                FROM pg_catalog.pg_sequence s
+                JOIN pg_catalog.pg_class c on s.seqrelid = c."oid"
+                WHERE c.relkind = 'S'
+                AND a.attidentity != ''
+                AND s.seqrelid = pg_catalog.pg_get_serial_sequence(
+                    a.attrelid::regclass::text, a.attname
+                )::regclass::oid
+                ) as identity_options\
+                """
+        else:
+            identity = "NULL as identity_options"
+
+        SQL_COLS = """
+            SELECT a.attname,
+              pg_catalog.format_type(a.atttypid, a.atttypmod),
+              (
+                SELECT pg_catalog.pg_get_expr(d.adbin, d.adrelid)
+                FROM pg_catalog.pg_attrdef d
+                WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum
+                AND a.atthasdef
+              ) AS DEFAULT,
+              a.attnotnull,
+              a.attrelid as table_oid,
+              pgd.description as comment,
+              %s,
+              %s
+            FROM pg_catalog.pg_attribute a
+            LEFT JOIN pg_catalog.pg_description pgd ON (
+                pgd.objoid = a.attrelid AND pgd.objsubid = a.attnum)
+            WHERE a.attrelid = :table_oid
+            AND a.attnum > 0 AND NOT a.attisdropped
+            ORDER BY a.attnum
+        """ % (
+            generated,
+            identity,
+        )
+        s = (
+            sql.text(SQL_COLS)
+            .bindparams(sql.bindparam("table_oid", type_=sqltypes.Integer))
+            .columns(attname=sqltypes.Unicode, default=sqltypes.Unicode)
+        )
+        c = connection.execute(s, dict(table_oid=table_oid))
+        rows = c.fetchall()
+
+        # dictionary with (name, ) if default search path or (schema, name)
+        # as keys
+        domains = self._load_domains(connection)
+
+        # dictionary with (name, ) if default search path or (schema, name)
+        # as keys
+        enums = dict(
+            ((rec["name"],), rec)
+            if rec["visible"]
+            else ((rec["schema"], rec["name"]), rec)
+            for rec in self._load_enums(connection, schema="*")
+        )
+
+        # format columns
+        columns = []
+
+        for (
+            name,
+            format_type,
+            default_,
+            notnull,
+            table_oid,
+            comment,
+            generated,
+            identity,
+        ) in rows:
+            column_info = self._get_column_info(
+                name,
+                format_type,
+                default_,
+                notnull,
+                domains,
+                enums,
+                schema,
+                comment,
+                generated,
+                identity,
+            )
+            columns.append(column_info)
+        return columns
+
+    def _get_column_info(
+        self,
+        name,
+        format_type,
+        default,
+        notnull,
+        domains,
+        enums,
+        schema,
+        comment,
+        generated,
+        identity,
+    ):
+        def _handle_array_type(attype):
+            return (
+                # strip '[]' from integer[], etc.
+                re.sub(r"\[\]$", "", attype),
+                attype.endswith("[]"),
+            )
+
+        # strip (*) from character varying(5), timestamp(5)
+        # with time zone, geometry(POLYGON), etc.
+        attype = re.sub(r"\(.*\)", "", format_type)
+
+        # strip '[]' from integer[], etc. and check if an array
+        attype, is_array = _handle_array_type(attype)
+
+        # strip quotes from case sensitive enum or domain names
+        enum_or_domain_key = tuple(util.quoted_token_parser(attype))
+
+        nullable = not notnull
+
+        charlen = re.search(r"\(([\d,]+)\)", format_type)
+        if charlen:
+            charlen = charlen.group(1)
+        args = re.search(r"\((.*)\)", format_type)
+        if args and args.group(1):
+            args = tuple(re.split(r"\s*,\s*", args.group(1)))
+        else:
+            args = ()
+        kwargs = {}
+
+        if attype == "numeric":
+            if charlen:
+                prec, scale = charlen.split(",")
+                args = (int(prec), int(scale))
+            else:
+                args = ()
+        elif attype == "double precision":
+            args = (53,)
+        elif attype == "integer":
+            args = ()
+        elif attype in ("timestamp with time zone", "time with time zone"):
+            kwargs["timezone"] = True
+            if charlen:
+                kwargs["precision"] = int(charlen)
+            args = ()
+        elif attype in (
+            "timestamp without time zone",
+            "time without time zone",
+            "time",
+        ):
+            kwargs["timezone"] = False
+            if charlen:
+                kwargs["precision"] = int(charlen)
+            args = ()
+        elif attype == "bit varying":
+            kwargs["varying"] = True
+            if charlen:
+                args = (int(charlen),)
+            else:
+                args = ()
+        elif attype.startswith("interval"):
+            field_match = re.match(r"interval (.+)", attype, re.I)
+            if charlen:
+                kwargs["precision"] = int(charlen)
+            if field_match:
+                kwargs["fields"] = field_match.group(1)
+            attype = "interval"
+            args = ()
+        elif charlen:
+            args = (int(charlen),)
+
+        while True:
+            # looping here to suit nested domains
+            if attype in self.ischema_names:
+                coltype = self.ischema_names[attype]
+                break
+            elif enum_or_domain_key in enums:
+                enum = enums[enum_or_domain_key]
+                coltype = ENUM
+                kwargs["name"] = enum["name"]
+                if not enum["visible"]:
+                    kwargs["schema"] = enum["schema"]
+                args = tuple(enum["labels"])
+                break
+            elif enum_or_domain_key in domains:
+                domain = domains[enum_or_domain_key]
+                attype = domain["attype"]
+                attype, is_array = _handle_array_type(attype)
+                # strip quotes from case sensitive enum or domain names
+                enum_or_domain_key = tuple(util.quoted_token_parser(attype))
+                # A table can't override a not null on the domain,
+                # but can override nullable
+                nullable = nullable and domain["nullable"]
+                if domain["default"] and not default:
+                    # It can, however, override the default
+                    # value, but can't set it to null.
+                    default = domain["default"]
+                continue
+            else:
+                coltype = None
+                break
+
+        if coltype:
+            coltype = coltype(*args, **kwargs)
+            if is_array:
+                coltype = self.ischema_names["_array"](coltype)
+        else:
+            util.warn(
+                "Did not recognize type '%s' of column '%s'" % (attype, name)
+            )
+            coltype = sqltypes.NULLTYPE
+
+        # If a zero byte or blank string depending on driver (is also absent
+        # for older PG versions), then not a generated column. Otherwise, s =
+        # stored. (Other values might be added in the future.)
+        if generated not in (None, "", b"\x00"):
+            computed = dict(
+                sqltext=default, persisted=generated in ("s", b"s")
+            )
+            default = None
+        else:
+            computed = None
+
+        # adjust the default value
+        autoincrement = False
+        if default is not None:
+            match = re.search(r"""(nextval\(')([^']+)('.*$)""", default)
+            if match is not None:
+                if issubclass(coltype._type_affinity, sqltypes.Integer):
+                    autoincrement = True
+                # the default is related to a Sequence
+                sch = schema
+                if "." not in match.group(2) and sch is not None:
+                    # unconditionally quote the schema name.  this could
+                    # later be enhanced to obey quoting rules /
+                    # "quote schema"
+                    default = (
+                        match.group(1)
+                        + ('"%s"' % sch)
+                        + "."
+                        + match.group(2)
+                        + match.group(3)
+                    )
+
+        column_info = dict(
+            name=name,
+            type=coltype,
+            nullable=nullable,
+            default=default,
+            autoincrement=autoincrement or identity is not None,
+            comment=comment,
+        )
+        if computed is not None:
+            column_info["computed"] = computed
+        if identity is not None:
+            column_info["identity"] = identity
+        return column_info
+
+    @reflection.cache
+    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        if self.server_version_info < (8, 4):
+            PK_SQL = """
+                SELECT a.attname
+                FROM
+                    pg_class t
+                    join pg_index ix on t.oid = ix.indrelid
+                    join pg_attribute a
+                        on t.oid=a.attrelid AND %s
+                 WHERE
+                  t.oid = :table_oid and ix.indisprimary = 't'
+                ORDER BY a.attnum
+            """ % self._pg_index_any(
+                "a.attnum", "ix.indkey"
+            )
+
+        else:
+            # unnest() and generate_subscripts() both introduced in
+            # version 8.4
+            PK_SQL = """
+                SELECT a.attname
+                FROM pg_attribute a JOIN (
+                    SELECT unnest(ix.indkey) attnum,
+                           generate_subscripts(ix.indkey, 1) ord
+                    FROM pg_index ix
+                    WHERE ix.indrelid = :table_oid AND ix.indisprimary
+                    ) k ON a.attnum=k.attnum
+                WHERE a.attrelid = :table_oid
+                ORDER BY k.ord
+            """
+        t = sql.text(PK_SQL).columns(attname=sqltypes.Unicode)
+        c = connection.execute(t, dict(table_oid=table_oid))
+        cols = [r[0] for r in c.fetchall()]
+
+        PK_CONS_SQL = """
+        SELECT conname
+           FROM  pg_catalog.pg_constraint r
+           WHERE r.conrelid = :table_oid AND r.contype = 'p'
+           ORDER BY 1
+        """
+        t = sql.text(PK_CONS_SQL).columns(conname=sqltypes.Unicode)
+        c = connection.execute(t, dict(table_oid=table_oid))
+        name = c.scalar()
+
+        return {"constrained_columns": cols, "name": name}
+
+    @reflection.cache
+    def get_foreign_keys(
+        self,
+        connection,
+        table_name,
+        schema=None,
+        postgresql_ignore_search_path=False,
+        **kw
+    ):
+        preparer = self.identifier_preparer
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        FK_SQL = """
+          SELECT r.conname,
+                pg_catalog.pg_get_constraintdef(r.oid, true) as condef,
+                n.nspname as conschema
+          FROM  pg_catalog.pg_constraint r,
+                pg_namespace n,
+                pg_class c
+
+          WHERE r.conrelid = :table AND
+                r.contype = 'f' AND
+                c.oid = confrelid AND
+                n.oid = c.relnamespace
+          ORDER BY 1
+        """
+        # https://www.postgresql.org/docs/9.0/static/sql-createtable.html
+        FK_REGEX = re.compile(
+            r"FOREIGN KEY \((.*?)\) REFERENCES (?:(.*?)\.)?(.*?)\((.*?)\)"
+            r"[\s]?(MATCH (FULL|PARTIAL|SIMPLE)+)?"
+            r"[\s]?(ON UPDATE "
+            r"(CASCADE|RESTRICT|NO ACTION|SET NULL|SET DEFAULT)+)?"
+            r"[\s]?(ON DELETE "
+            r"(CASCADE|RESTRICT|NO ACTION|SET NULL|SET DEFAULT)+)?"
+            r"[\s]?(DEFERRABLE|NOT DEFERRABLE)?"
+            r"[\s]?(INITIALLY (DEFERRED|IMMEDIATE)+)?"
+        )
+
+        t = sql.text(FK_SQL).columns(
+            conname=sqltypes.Unicode, condef=sqltypes.Unicode
+        )
+        c = connection.execute(t, dict(table=table_oid))
+        fkeys = []
+        for conname, condef, conschema in c.fetchall():
+            m = re.search(FK_REGEX, condef).groups()
+
+            (
+                constrained_columns,
+                referred_schema,
+                referred_table,
+                referred_columns,
+                _,
+                match,
+                _,
+                onupdate,
+                _,
+                ondelete,
+                deferrable,
+                _,
+                initially,
+            ) = m
+
+            if deferrable is not None:
+                deferrable = True if deferrable == "DEFERRABLE" else False
+            constrained_columns = [
+                preparer._unquote_identifier(x)
+                for x in re.split(r"\s*,\s*", constrained_columns)
+            ]
+
+            if postgresql_ignore_search_path:
+                # when ignoring search path, we use the actual schema
+                # provided it isn't the "default" schema
+                if conschema != self.default_schema_name:
+                    referred_schema = conschema
+                else:
+                    referred_schema = schema
+            elif referred_schema:
+                # referred_schema is the schema that we regexp'ed from
+                # pg_get_constraintdef().  If the schema is in the search
+                # path, pg_get_constraintdef() will give us None.
+                referred_schema = preparer._unquote_identifier(referred_schema)
+            elif schema is not None and schema == conschema:
+                # If the actual schema matches the schema of the table
+                # we're reflecting, then we will use that.
+                referred_schema = schema
+
+            referred_table = preparer._unquote_identifier(referred_table)
+            referred_columns = [
+                preparer._unquote_identifier(x)
+                for x in re.split(r"\s*,\s", referred_columns)
+            ]
+            options = {
+                k: v
+                for k, v in [
+                    ("onupdate", onupdate),
+                    ("ondelete", ondelete),
+                    ("initially", initially),
+                    ("deferrable", deferrable),
+                    ("match", match),
+                ]
+                if v is not None and v != "NO ACTION"
+            }
+            fkey_d = {
+                "name": conname,
+                "constrained_columns": constrained_columns,
+                "referred_schema": referred_schema,
+                "referred_table": referred_table,
+                "referred_columns": referred_columns,
+                "options": options,
+            }
+            fkeys.append(fkey_d)
+        return fkeys
+
+    def _pg_index_any(self, col, compare_to):
+        if self.server_version_info < (8, 1):
+            # https://www.postgresql.org/message-id/10279.1124395722@sss.pgh.pa.us
+            # "In CVS tip you could replace this with "attnum = ANY (indkey)".
+            # Unfortunately, most array support doesn't work on int2vector in
+            # pre-8.1 releases, so I think you're kinda stuck with the above
+            # for now.
+            # regards, tom lane"
+            return "(%s)" % " OR ".join(
+                "%s[%d] = %s" % (compare_to, ind, col) for ind in range(0, 10)
+            )
+        else:
+            return "%s = ANY(%s)" % (col, compare_to)
+
+    @reflection.cache
+    def get_indexes(self, connection, table_name, schema, **kw):
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        # cast indkey as varchar since it's an int2vector,
+        # returned as a list by some drivers such as pypostgresql
+
+        if self.server_version_info < (8, 5):
+            IDX_SQL = """
+              SELECT
+                  i.relname as relname,
+                  ix.indisunique, ix.indexprs, ix.indpred,
+                  a.attname, a.attnum, NULL, ix.indkey%s,
+                  %s, %s, am.amname,
+                  NULL as indnkeyatts
+              FROM
+                  pg_class t
+                        join pg_index ix on t.oid = ix.indrelid
+                        join pg_class i on i.oid = ix.indexrelid
+                        left outer join
+                            pg_attribute a
+                            on t.oid = a.attrelid and %s
+                        left outer join
+                            pg_am am
+                            on i.relam = am.oid
+              WHERE
+                  t.relkind IN ('r', 'v', 'f', 'm')
+                  and t.oid = :table_oid
+                  and ix.indisprimary = 'f'
+              ORDER BY
+                  t.relname,
+                  i.relname
+            """ % (
+                # version 8.3 here was based on observing the
+                # cast does not work in PG 8.2.4, does work in 8.3.0.
+                # nothing in PG changelogs regarding this.
+                "::varchar" if self.server_version_info >= (8, 3) else "",
+                "ix.indoption::varchar"
+                if self.server_version_info >= (8, 3)
+                else "NULL",
+                "i.reloptions"
+                if self.server_version_info >= (8, 2)
+                else "NULL",
+                self._pg_index_any("a.attnum", "ix.indkey"),
+            )
+        else:
+            IDX_SQL = """
+              SELECT
+                  i.relname as relname,
+                  ix.indisunique, ix.indexprs,
+                  a.attname, a.attnum, c.conrelid, ix.indkey::varchar,
+                  ix.indoption::varchar, i.reloptions, am.amname,
+                  pg_get_expr(ix.indpred, ix.indrelid),
+                  %s as indnkeyatts
+              FROM
+                  pg_class t
+                        join pg_index ix on t.oid = ix.indrelid
+                        join pg_class i on i.oid = ix.indexrelid
+                        left outer join
+                            pg_attribute a
+                            on t.oid = a.attrelid and a.attnum = ANY(ix.indkey)
+                        left outer join
+                            pg_constraint c
+                            on (ix.indrelid = c.conrelid and
+                                ix.indexrelid = c.conindid and
+                                c.contype in ('p', 'u', 'x'))
+                        left outer join
+                            pg_am am
+                            on i.relam = am.oid
+              WHERE
+                  t.relkind IN ('r', 'v', 'f', 'm', 'p')
+                  and t.oid = :table_oid
+                  and ix.indisprimary = 'f'
+              ORDER BY
+                  t.relname,
+                  i.relname
+            """ % (
+                "ix.indnkeyatts"
+                if self.server_version_info >= (11, 0)
+                else "NULL",
+            )
+
+        t = sql.text(IDX_SQL).columns(
+            relname=sqltypes.Unicode, attname=sqltypes.Unicode
+        )
+        c = connection.execute(t, dict(table_oid=table_oid))
+
+        indexes = defaultdict(lambda: defaultdict(dict))
+
+        sv_idx_name = None
+        for row in c.fetchall():
+            (
+                idx_name,
+                unique,
+                expr,
+                col,
+                col_num,
+                conrelid,
+                idx_key,
+                idx_option,
+                options,
+                amname,
+                filter_definition,
+                indnkeyatts,
+            ) = row
+
+            if expr:
+                if idx_name != sv_idx_name:
+                    util.warn(
+                        "Skipped unsupported reflection of "
+                        "expression-based index %s" % idx_name
+                    )
+                sv_idx_name = idx_name
+                continue
+
+            has_idx = idx_name in indexes
+            index = indexes[idx_name]
+            if col is not None:
+                index["cols"][col_num] = col
+            if not has_idx:
+                idx_keys = idx_key.split()
+                # "The number of key columns in the index, not counting any
+                # included columns, which are merely stored and do not
+                # participate in the index semantics"
+                if indnkeyatts and idx_keys[indnkeyatts:]:
+                    # this is a "covering index" which has INCLUDE columns
+                    # as well as regular index columns
+                    inc_keys = idx_keys[indnkeyatts:]
+                    idx_keys = idx_keys[:indnkeyatts]
+                else:
+                    inc_keys = []
+
+                index["key"] = [int(k.strip()) for k in idx_keys]
+                index["inc"] = [int(k.strip()) for k in inc_keys]
+
+                # (new in pg 8.3)
+                # "pg_index.indoption" is list of ints, one per column/expr.
+                # int acts as bitmask: 0x01=DESC, 0x02=NULLSFIRST
+                sorting = {}
+                for col_idx, col_flags in enumerate(
+                    (idx_option or "").split()
+                ):
+                    col_flags = int(col_flags.strip())
+                    col_sorting = ()
+                    # try to set flags only if they differ from PG defaults...
+                    if col_flags & 0x01:
+                        col_sorting += ("desc",)
+                        if not (col_flags & 0x02):
+                            col_sorting += ("nulls_last",)
+                    else:
+                        if col_flags & 0x02:
+                            col_sorting += ("nulls_first",)
+                    if col_sorting:
+                        sorting[col_idx] = col_sorting
+                if sorting:
+                    index["sorting"] = sorting
+
+                index["unique"] = unique
+                if conrelid is not None:
+                    index["duplicates_constraint"] = idx_name
+                if options:
+                    index["options"] = dict(
+                        [option.split("=") for option in options]
+                    )
+
+                # it *might* be nice to include that this is 'btree' in the
+                # reflection info.  But we don't want an Index object
+                # to have a ``postgresql_using`` in it that is just the
+                # default, so for the moment leaving this out.
+                if amname and amname != "btree":
+                    index["amname"] = amname
+
+                if filter_definition:
+                    index["postgresql_where"] = filter_definition
+
+        result = []
+        for name, idx in indexes.items():
+            entry = {
+                "name": name,
+                "unique": idx["unique"],
+                "column_names": [idx["cols"][i] for i in idx["key"]],
+            }
+            if self.server_version_info >= (11, 0):
+                # NOTE: this is legacy, this is part of dialect_options now
+                # as of #7382
+                entry["include_columns"] = [idx["cols"][i] for i in idx["inc"]]
+            if "duplicates_constraint" in idx:
+                entry["duplicates_constraint"] = idx["duplicates_constraint"]
+            if "sorting" in idx:
+                entry["column_sorting"] = dict(
+                    (idx["cols"][idx["key"][i]], value)
+                    for i, value in idx["sorting"].items()
+                )
+            if "include_columns" in entry:
+                entry.setdefault("dialect_options", {})[
+                    "postgresql_include"
+                ] = entry["include_columns"]
+            if "options" in idx:
+                entry.setdefault("dialect_options", {})[
+                    "postgresql_with"
+                ] = idx["options"]
+            if "amname" in idx:
+                entry.setdefault("dialect_options", {})[
+                    "postgresql_using"
+                ] = idx["amname"]
+            if "postgresql_where" in idx:
+                entry.setdefault("dialect_options", {})[
+                    "postgresql_where"
+                ] = idx["postgresql_where"]
+            result.append(entry)
+        return result
+
+    @reflection.cache
+    def get_unique_constraints(
+        self, connection, table_name, schema=None, **kw
+    ):
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        UNIQUE_SQL = """
+            SELECT
+                cons.conname as name,
+                cons.conkey as key,
+                a.attnum as col_num,
+                a.attname as col_name
+            FROM
+                pg_catalog.pg_constraint cons
+                join pg_attribute a
+                  on cons.conrelid = a.attrelid AND
+                    a.attnum = ANY(cons.conkey)
+            WHERE
+                cons.conrelid = :table_oid AND
+                cons.contype = 'u'
+        """
+
+        t = sql.text(UNIQUE_SQL).columns(col_name=sqltypes.Unicode)
+        c = connection.execute(t, dict(table_oid=table_oid))
+
+        uniques = defaultdict(lambda: defaultdict(dict))
+        for row in c.fetchall():
+            uc = uniques[row.name]
+            uc["key"] = row.key
+            uc["cols"][row.col_num] = row.col_name
+
+        return [
+            {"name": name, "column_names": [uc["cols"][i] for i in uc["key"]]}
+            for name, uc in uniques.items()
+        ]
+
+    @reflection.cache
+    def get_table_comment(self, connection, table_name, schema=None, **kw):
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        COMMENT_SQL = """
+            SELECT
+                pgd.description as table_comment
+            FROM
+                pg_catalog.pg_description pgd
+            WHERE
+                pgd.objsubid = 0 AND
+                pgd.objoid = :table_oid
+        """
+
+        c = connection.execute(
+            sql.text(COMMENT_SQL), dict(table_oid=table_oid)
+        )
+        return {"text": c.scalar()}
+
+    @reflection.cache
+    def get_check_constraints(self, connection, table_name, schema=None, **kw):
+        table_oid = self.get_table_oid(
+            connection, table_name, schema, info_cache=kw.get("info_cache")
+        )
+
+        CHECK_SQL = """
+            SELECT
+                cons.conname as name,
+                pg_get_constraintdef(cons.oid) as src
+            FROM
+                pg_catalog.pg_constraint cons
+            WHERE
+                cons.conrelid = :table_oid AND
+                cons.contype = 'c'
+        """
+
+        c = connection.execute(sql.text(CHECK_SQL), dict(table_oid=table_oid))
+
+        ret = []
+        for name, src in c:
+            # samples:
+            # "CHECK (((a > 1) AND (a < 5)))"
+            # "CHECK (((a = 1) OR ((a > 2) AND (a < 5))))"
+            # "CHECK (((a > 1) AND (a < 5))) NOT VALID"
+            # "CHECK (some_boolean_function(a))"
+            # "CHECK (((a\n < 1)\n OR\n (a\n >= 5))\n)"
+
+            m = re.match(
+                r"^CHECK *\((.+)\)( NOT VALID)?$", src, flags=re.DOTALL
+            )
+            if not m:
+                util.warn("Could not parse CHECK constraint text: %r" % src)
+                sqltext = ""
+            else:
+                sqltext = re.compile(
+                    r"^[\s\n]*\((.+)\)[\s\n]*$", flags=re.DOTALL
+                ).sub(r"\1", m.group(1))
+            entry = {"name": name, "sqltext": sqltext}
+            if m and m.group(2):
+                entry["dialect_options"] = {"not_valid": True}
+
+            ret.append(entry)
+        return ret
+
+    def _load_enums(self, connection, schema=None):
+        schema = schema or self.default_schema_name
+        if not self.supports_native_enum:
+            return {}
+
+        # Load data types for enums:
+        SQL_ENUMS = """
+            SELECT t.typname as "name",
+               -- no enum defaults in 8.4 at least
+               -- t.typdefault as "default",
+               pg_catalog.pg_type_is_visible(t.oid) as "visible",
+               n.nspname as "schema",
+               e.enumlabel as "label"
+            FROM pg_catalog.pg_type t
+                 LEFT JOIN pg_catalog.pg_namespace n ON n.oid = t.typnamespace
+                 LEFT JOIN pg_catalog.pg_enum e ON t.oid = e.enumtypid
+            WHERE t.typtype = 'e'
+        """
+
+        if schema != "*":
+            SQL_ENUMS += "AND n.nspname = :schema "
+
+        # e.oid gives us label order within an enum
+        SQL_ENUMS += 'ORDER BY "schema", "name", e.oid'
+
+        s = sql.text(SQL_ENUMS).columns(
+            attname=sqltypes.Unicode, label=sqltypes.Unicode
+        )
+
+        if schema != "*":
+            s = s.bindparams(schema=schema)
+
+        c = connection.execute(s)
+
+        enums = []
+        enum_by_name = {}
+        for enum in c.fetchall():
+            key = (enum.schema, enum.name)
+            if key in enum_by_name:
+                enum_by_name[key]["labels"].append(enum.label)
+            else:
+                enum_by_name[key] = enum_rec = {
+                    "name": enum.name,
+                    "schema": enum.schema,
+                    "visible": enum.visible,
+                    "labels": [],
+                }
+                if enum.label is not None:
+                    enum_rec["labels"].append(enum.label)
+                enums.append(enum_rec)
+        return enums
+
+    def _load_domains(self, connection):
+        # Load data types for domains:
+        SQL_DOMAINS = """
+            SELECT t.typname as "name",
+               pg_catalog.format_type(t.typbasetype, t.typtypmod) as "attype",
+               not t.typnotnull as "nullable",
+               t.typdefault as "default",
+               pg_catalog.pg_type_is_visible(t.oid) as "visible",
+               n.nspname as "schema"
+            FROM pg_catalog.pg_type t
+               LEFT JOIN pg_catalog.pg_namespace n ON n.oid = t.typnamespace
+            WHERE t.typtype = 'd'
+        """
+
+        s = sql.text(SQL_DOMAINS)
+        c = connection.execution_options(future_result=True).execute(s)
+
+        domains = {}
+        for domain in c.mappings():
+            domain = domain
+            # strip (30) from character varying(30)
+            attype = re.search(r"([^\(]+)", domain["attype"]).group(1)
+            # 'visible' just means whether or not the domain is in a
+            # schema that's on the search path -- or not overridden by
+            # a schema with higher precedence. If it's not visible,
+            # it will be prefixed with the schema-name when it's used.
+            if domain["visible"]:
+                key = (domain["name"],)
+            else:
+                key = (domain["schema"], domain["name"])
+
+            domains[key] = {
+                "attype": attype,
+                "nullable": domain["nullable"],
+                "default": domain["default"],
+            }
+
+        return domains