text: # postgresql/base.py
  # Copyright (C) 2005-2020 the SQLAlchemy authors and contributors
  # <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  r"""
  .. dialect:: postgresql
      :name: PostgreSQL
  
  .. _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 IDENTITY columns
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  
  PostgreSQL 10 has a new IDENTITY feature that supersedes the use of SERIAL.
  Built-in support for rendering of IDENTITY is not available yet, however the
  following compilation hook may be used 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 NOT NULL,
          data VARCHAR,
          PRIMARY KEY (id)
      )
  
  .. _postgresql_isolation_level:
  
  Transaction Isolation Level
  ---------------------------
  
  Most SQLAlchemy dialects support setting of transaction isolation level
  using the :paramref:`_sa.create_engine.execution_options` 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",
          execution_options={
              "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
  
  Valid values for ``isolation_level`` on most PostgreSQL dialects include:
  
  * ``READ COMMITTED``
  * ``READ UNCOMMITTED``
  * ``REPEATABLE READ``
  * ``SERIALIZABLE``
  * ``AUTOCOMMIT``
  
  .. seealso::
  
      :ref:`dbapi_autocommit`
  
      :ref:`psycopg2_isolation_level`
  
      :ref:`pg8000_isolation_level`
  
  .. _postgresql_schema_reflection:
  
  Remote-Schema Table Introspection and PostgreSQL search_path
  ------------------------------------------------------------
  
  **TL;DR;**: keep the ``search_path`` variable set to its default of ``public``,
  name schemas **other** than ``public`` explicitly within ``Table`` definitions.
  
  The PostgreSQL dialect can reflect tables from any schema.  The
  :paramref:`_schema.Table.schema` argument, or alternatively the
  :paramref:`.MetaData.reflect.schema` argument determines which schema will
  be searched for the table or tables.   The reflected :class:`_schema.Table`
  objects
  will in all cases retain this ``.schema`` attribute as was specified.
  However, 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
  <http://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
      >>> engine = create_engine("postgresql://scott:tiger@localhost/test")
      >>> with engine.connect() as conn:
      ...     conn.execute("SET search_path TO test_schema, public")
      ...     meta = MetaData()
      ...     referring = Table('referring', meta,
      ...                       autoload=True, autoload_with=conn)
      ...
      <sqlalchemy.engine.result.ResultProxy object at 0x101612ed0>
  
  The above process would deliver to the :attr:`_schema.MetaData.tables`
  collection
  ``referred`` table named **without** the schema::
  
      >>> meta.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("SET search_path TO test_schema, public")
      ...     meta = MetaData()
      ...     referring = Table('referring', meta, autoload=True,
      ...                       autoload_with=conn,
      ...                       postgresql_ignore_search_path=True)
      ...
      <sqlalchemy.engine.result.ResultProxy object at 0x1016126d0>
  
  We will now have ``test_schema.referred`` stored as schema-qualified::
  
      >>> meta.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``.
  
  .. versionadded:: 0.9.2 Added the ``postgresql_ignore_search_path``
     dialect-level option accepted by :class:`_schema.Table` and
     :meth:`_schema.MetaData.reflect`.
  
  
  .. seealso::
  
      `The Schema Search Path
      <http://www.postgresql.org/docs/9.0/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`::
  
      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']
      )
  
      conn.execute(do_nothing_stmt)
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          constraint='pk_my_table',
          set_=dict(data='updated value')
      )
  
      conn.execute(do_update_stmt)
  
  Both methods supply the "target" of the conflict using either the
  named constraint or by column inference:
  
  * The :paramref:`.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::
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          index_elements=['id'],
          set_=dict(data='updated value')
      )
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          index_elements=[my_table.c.id],
          set_=dict(data='updated value')
      )
  
  * When using :paramref:`.Insert.on_conflict_do_update.index_elements` to
    infer an index, a partial index can be inferred by also specifying the
    use the :paramref:`.Insert.on_conflict_do_update.index_where` parameter::
  
      from sqlalchemy.dialects.postgresql import insert
  
      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)
          )
      conn.execute(stmt)
  
  * The :paramref:`.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::
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          constraint='my_table_idx_1',
          set_=dict(data='updated value')
      )
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          constraint='my_table_pk',
          set_=dict(data='updated value')
      )
  
  * The :paramref:`.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::
  
      do_update_stmt = insert_stmt.on_conflict_do_update(
          constraint=my_table.primary_key,
          set_=dict(data='updated value')
      )
  
  ``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:`.Insert.on_conflict_do_update.set_` parameter.  This
  parameter accepts a dictionary which consists of direct values
  for UPDATE::
  
      from sqlalchemy.dialects.postgresql import insert
  
      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')
          )
      conn.execute(do_update_stmt)
  
  .. 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:`.Insert.on_conflict_do_update.set_` dictionary.
  
  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::
  
      from sqlalchemy.dialects.postgresql import insert
  
      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)
          )
      conn.execute(do_update_stmt)
  
  The :meth:`_expression.Insert.on_conflict_do_update` method also accepts
  a WHERE clause using the :paramref:`.Insert.on_conflict_do_update.where`
  parameter, which will limit those rows which receive an UPDATE::
  
      from sqlalchemy.dialects.postgresql import insert
  
      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)
          )
      conn.execute(on_update_stmt)
  
  ``ON CONFLICT`` may also 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::
  
      from sqlalchemy.dialects.postgresql import insert
  
      stmt = insert(my_table).values(id='some_id', data='inserted value')
      stmt = stmt.on_conflict_do_nothing(index_elements=['id'])
      conn.execute(stmt)
  
  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::
  
      from sqlalchemy.dialects.postgresql import insert
  
      stmt = insert(my_table).values(id='some_id', data='inserted value')
      stmt = stmt.on_conflict_do_nothing()
      conn.execute(stmt)
  
  .. versionadded:: 1.1 Added support for PostgreSQL ON CONFLICT clauses
  
  .. seealso::
  
      `INSERT .. ON CONFLICT
      <http://www.postgresql.org/docs/current/static/sql-insert.html#SQL-ON-CONFLICT>`_
      - in the PostgreSQL documentation.
  
  .. _postgresql_match:
  
  Full Text Search
  ----------------
  
  SQLAlchemy makes available the PostgreSQL ``@@`` operator via the
  :meth:`_expression.ColumnElement.match`
  method on any textual column expression.
  On a 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
  
  The PostgreSQL text search functions such as ``to_tsquery()``
  and ``to_tsvector()`` are available
  explicitly using the standard :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
  
  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.
  
  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.
  
  .. _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
  http://www.postgresql.org/docs/8.3/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
  http://www.postgresql.org/docs/8.3/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=True)``, 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
      <http://www.postgresql.org/docs/current/static/sql-createtable.html>`_
  
  Table values, Row and Tuple objects
  -----------------------------------
  
  Row Types
  ^^^^^^^^^
  
  Built-in support for rendering a ``ROW`` is not available yet, however the
  :func:`_expression.tuple_` may be used in its place. Another alternative is
  to use the :attr:`_sa.func` generator with ``func.ROW`` ::
  
      table.select().where(
          tuple_(table.c.id, table.c.fk) > (1,2)
      ).where(func.ROW(table.c.id, table.c.fk) < func.ROW(3, 7))
  
  Will generate the row-wise comparison::
  
      SELECT *
      FROM table
      WHERE (id, fk) > (1, 2)
      AND ROW(id, fk) < ROW(3, 7)
  
  .. 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
  ^^^^^^^^^^^
  
  PostgreSQL also supports passing a table as an argument to a function. This
  is not available yet in sqlalchemy, however the
  :func:`_expression.literal_column` function with the name of the table may be
  used in its place::
  
      select(['*']).select_from(func.my_function(literal_column('my_table')))
  
  Will generate the SQL::
  
      SELECT *
      FROM my_function(my_table)
  
  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 accomodate
  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))
      )
  
  
  """
  from collections import defaultdict
  import datetime as dt
  import re
  
  from . import array as _array
  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 default
  from ...engine import reflection
  from ...sql import compiler
  from ...sql import elements
  from ...sql import expression
  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
  
  
  try:
      from uuid import UUID as _python_UUID  # noqa
  except ImportError:
      _python_UUID = None
  
  
  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):
  
      """Provide the PostgreSQL MONEY type.
  
      .. 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):
      def __init__(self, timezone=False, precision=None):
          super(TIMESTAMP, self).__init__(timezone=timezone)
          self.precision = precision
  
  
  class TIME(sqltypes.TIME):
      def __init__(self, timezone=False, precision=None):
          super(TIME, self).__init__(timezone=timezone)
          self.precision = precision
  
  
  class INTERVAL(sqltypes.NativeForEmulated, sqltypes._AbstractInterval):
  
      """PostgreSQL INTERVAL type.
  
      The INTERVAL type may not be supported on all DBAPIs.
      It is known to work on psycopg2 and not pg8000 or zxjdbc.
  
      """
  
      __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
  
      @property
      def python_type(self):
          return dt.timedelta
  
  
  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 may not be supported on all DBAPIs.
      It is known to work on psycopg2 and not pg8000.
  
      """
  
      __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.
  
          """
          if as_uuid and _python_UUID is None:
              raise NotImplementedError(
                  "This version of Python does not support "
                  "the native UUID type."
              )
          self.as_uuid = as_uuid
  
      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
  
  
  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.
  
          """
          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)
          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_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_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)
  
  
  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_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_notilike_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 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):
          if select._distinct is not False:
              if select._distinct is True:
                  return "DISTINCT "
              elif isinstance(select._distinct, (list, tuple)):
                  return (
                      "DISTINCT ON ("
                      + ", ".join(
                          [self.process(col, **kw) for col in select._distinct]
                      )
                      + ") "
                  )
              else:
                  return (
                      "DISTINCT ON ("
                      + self.process(select._distinct, **kw)
                      + ") "
                  )
          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_select_column(None, c, True, False, {})
              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_text = "ON CONSTRAINT %s" % 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
  
      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)
                  if elements._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(col_key)
                  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(
                      elements._literal_as_binds(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
      ):
          return "FROM " + ", ".join(
              t._compiler_dispatch(self, asfrom=True, 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."""
          return "USING " + ", ".join(
              t._compiler_dispatch(self, asfrom=True, fromhints=from_hints, **kw)
              for t in extra_froms
          )
  
  
  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
  
          if (
              column.primary_key
              and column is column.table._autoincrement_column
              and (
                  self.dialect.supports_smallserial
                  or not isinstance(impl_type, sqltypes.SmallInteger)
              )
              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 not column.nullable:
              colspec += " NOT NULL"
          return colspec
  
      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."
                  )
  
          return super(PGDDLCompiler, self).visit_check_constraint(constraint)
  
      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 "
  
          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
                  ]
              )
          )
  
          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:
              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 "
  
          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
          )
  
  
  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):
  
          # TODO: pass **kw?
          inner = self.process(type_.item_type)
          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 __init__(self, conn):
          reflection.Inspector.__init__(self, conn)
  
      def get_table_oid(self, table_name, schema=None):
          """Return the OID for the given table name."""
  
          return self.dialect.get_table_oid(
              self.bind, 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
          return self.dialect._load_enums(self.bind, 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
          return self.dialect._get_foreign_table_names(self.bind, 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
  
          """
  
          return self.dialect.get_view_names(
              self.bind, 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.dialect.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 PGDialect(default.DefaultDialect):
      name = "postgresql"
      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_empty_insert = False
      supports_multivalues_insert = 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
  
      construct_arguments = [
          (
              schema.Index,
              {
                  "using": False,
                  "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,
              },
          ),
      ]
  
      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)
          self.implicit_returning = (
              self.server_version_info
              > (
                  8,
                  2,
              )
              and self.__dict__.get("implicit_returning", True)
          )
          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)
  
          # http://www.postgresql.org/docs/9.3/static/release-9-2.html#AEN116689
          self.supports_smallserial = self.server_version_info >= (9, 2)
  
          self._backslash_escapes = (
              self.server_version_info < (8, 2)
              or connection.scalar("show standard_conforming_strings") == "off"
          )
  
          self._supports_create_index_concurrently = (
              self.server_version_info >= (8, 2)
          )
          self._supports_drop_index_concurrently = self.server_version_info >= (
              9,
              2,
          )
  
      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 do_begin_twophase(self, connection, xid):
          self.do_begin(connection.connection)
  
      def do_prepare_twophase(self, connection, xid):
          connection.execute("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.execute("ROLLBACK")
              connection.execute("ROLLBACK PREPARED '%s'" % xid)
              connection.execute("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.execute("ROLLBACK")
              connection.execute("COMMIT PREPARED '%s'" % xid)
              connection.execute("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.scalar("select current_schema()")
  
      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):
          # 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:
              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=current_schema() "
                      "and relname=:name"
                  ).bindparams(
                      sql.bindparam(
                          "name",
                          util.text_type(sequence_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 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.execute("select 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, 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),
              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),
              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),
              schema=schema if schema is not None else self.default_schema_name,
          )
          return [name for name, in result]
  
      @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),
              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"
          )
          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.attnum, a.attrelid as table_oid,
                pgd.description as comment,
                %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
          )
          s = (
              sql.text(SQL_COLS)
              .bindparams(sql.bindparam("table_oid", type_=sqltypes.Integer))
              .columns(attname=sqltypes.Unicode, default=sqltypes.Unicode)
          )
          c = connection.execute(s, 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,
              attnum,
              table_oid,
              comment,
              generated,
          ) in rows:
              column_info = self._get_column_info(
                  name,
                  format_type,
                  default_,
                  notnull,
                  domains,
                  enums,
                  schema,
                  comment,
                  generated,
              )
              columns.append(column_info)
          return columns
  
      def _get_column_info(
          self,
          name,
          format_type,
          default,
          notnull,
          domains,
          enums,
          schema,
          comment,
          generated,
      ):
          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 whether the domain is nullable.
                  nullable = 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 (''), then not a generated column.
          # Otherwise, s = stored. (Other values might be added in the future.)
          if generated:
              computed = dict(sqltext=default, persisted=generated == "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,
              comment=comment,
          )
          if computed is not None:
              column_info["computed"] = computed
          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, 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, 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
          """
          # http://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, 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)
              ]
              fkey_d = {
                  "name": conname,
                  "constrained_columns": constrained_columns,
                  "referred_schema": referred_schema,
                  "referred_table": referred_table,
                  "referred_columns": referred_columns,
                  "options": {
                      "onupdate": onupdate,
                      "ondelete": ondelete,
                      "deferrable": deferrable,
                      "initially": initially,
                      "match": match,
                  },
              }
              fkeys.append(fkey_d)
          return fkeys
  
      def _pg_index_any(self, col, compare_to):
          if self.server_version_info < (8, 1):
              # http://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, ix.indpred,
                    a.attname, a.attnum, c.conrelid, ix.indkey::varchar,
                    ix.indoption::varchar, i.reloptions, am.amname,
                    %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, table_oid=table_oid)
  
          indexes = defaultdict(lambda: defaultdict(dict))
  
          sv_idx_name = None
          for row in c.fetchall():
              (
                  idx_name,
                  unique,
                  expr,
                  prd,
                  col,
                  col_num,
                  conrelid,
                  idx_key,
                  idx_option,
                  options,
                  amname,
                  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
  
              if prd and not idx_name == sv_idx_name:
                  util.warn(
                      "Predicate of partial index %s ignored during reflection"
                      % idx_name
                  )
                  sv_idx_name = idx_name
  
              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:]:
                      util.warn(
                          "INCLUDE columns for covering index %s "
                          "ignored during reflection" % (idx_name,)
                      )
                      idx_keys = idx_keys[:indnkeyatts]
  
                  index["key"] = [int(k.strip()) for k in idx_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 += ("nullslast",)
                      else:
                          if col_flags & 0x02:
                              col_sorting += ("nullsfirst",)
                      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
  
          result = []
          for name, idx in indexes.items():
              entry = {
                  "name": name,
                  "unique": idx["unique"],
                  "column_names": [idx["cols"][i] for i in idx["key"]],
              }
              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 "options" in idx:
                  entry.setdefault("dialect_options", {})[
                      "postgresql_with"
                  ] = idx["options"]
              if "amname" in idx:
                  entry.setdefault("dialect_options", {})[
                      "postgresql_using"
                  ] = idx["amname"]
              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, 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), 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), 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).columns(attname=sqltypes.Unicode)
          c = connection.execute(s)
  
          domains = {}
          for domain in c.fetchall():
              # 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
  