# postgresql/base.py
# Copyright (C) 2005-2019 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:`.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
---------------------------

All PostgreSQL dialects support setting of transaction isolation level
both via a dialect-specific parameter
:paramref:`.create_engine.isolation_level` accepted by :func:`.create_engine`,
as well as the :paramref:`.Connection.execution_options.isolation_level`
argument as passed to :meth:`.Connection.execution_options`.
When using a non-psycopg2 dialect, this feature works by issuing the command
``SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL <level>`` for
each new connection.  For the special AUTOCOMMIT isolation level,
DBAPI-specific techniques are used.

To set isolation level using :func:`.create_engine`::

    engine = create_engine(
        "postgresql+pg8000://scott:tiger@localhost/test",
        isolation_level="READ UNCOMMITTED"
    )

To set using per-connection execution options::

    connection = engine.connect()
    connection = connection.execution_options(
        isolation_level="READ COMMITTED"
    )

Valid values for ``isolation_level`` include:

* ``READ COMMITTED``
* ``READ UNCOMMITTED``
* ``REPEATABLE READ``
* ``SERIALIZABLE``
* ``AUTOCOMMIT`` - on psycopg2 / pg8000 only

.. seealso::

    :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:`.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:`.Table` objects
will in all cases retain this ``.schema`` attribute as was specified.
However, with regards to tables which these :class:`.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:`.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:`.Table` as well as
:meth:`.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:`.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:`.Table` and
   :meth:`.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.dml.insert()` function, which provides
the generative methods :meth:`~.postgresql.dml.Insert.on_conflict_do_update`
and :meth:`~.postgresql.dml.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:`.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:`.Table` using the
  :attr:`.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:`.Insert.on_conflict_do_update` method does **not** take into
    account Python-side default UPDATE values or generation functions, e.g.
    e.g. those specified using :paramref:`.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.dml.Insert.excluded` is available as an attribute on
the :class:`.postgresql.dml.Insert` object; this object is a
:class:`.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:`.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.dml.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:`.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)

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`` dictionary are the "key" name of
the :class:`.Column`, i.e. the name used to access it from the ``.c``
collection of :class:`.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'
        })


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:`.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:`.Inspector`, the :meth:`.Inspector.get_indexes`
and the :meth:`.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:`.Table.indexes` when it is detected as mirroring a
:class:`.UniqueConstraint` in the :attr:`.Table.constraints` collection.

.. versionchanged:: 1.0.0 - :class:`.Table` reflection now includes
   :class:`.UniqueConstraint` objects present in the :attr:`.Table.constraints`
   collection; the PostgreSQL backend will no longer include a "mirrored"
   :class:`.Index` construct in :attr:`.Table.indexes` if it is detected
   as corresponding to a unique constraint.

Special Reflection Options
--------------------------

The :class:`.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:`.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>`_

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.   In order to send and receive an ARRAY of ENUM,
use the following workaround type::

    class ArrayOfEnum(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, for an ARRAY of JSON/JSONB we need to render the
appropriate CAST, however current psycopg2 drivers seem to handle the result
for ARRAY of JSON automatically, so the type is simpler::


    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 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 ...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


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:`.Table.create` and :meth:`.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:`.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`,
         :class:`.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

        if not checkfirst or not bind.dialect.has_type(
            bind, self.name, schema=self.schema
        ):
            bind.execute(CreateEnumType(self))

    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`,
         :class:`.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

        if not checkfirst or bind.dialect.has_type(
            bind, self.name, schema=self.schema
        ):
            bind.execute(DropEnumType(self))

    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.Interval: INTERVAL, sqltypes.Enum: ENUM}

ischema_names = {
    "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, **kw):
        kw["eager_grouping"] = True
        return self._generate_generic_binary(binary, " -> ", **kw)

    def visit_json_path_getitem_op_binary(self, binary, operator, **kw):
        kw["eager_grouping"] = True
        return self._generate_generic_binary(binary, " #> ", **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(
                c.table if isinstance(c, expression.ColumnClause) else c
                for c in select._for_update_arg.of
            )
            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.statement.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
            )
            default = self.get_column_default_string(column)
            if default is not None:
                colspec += " DEFAULT " + default

        if not column.nullable:
            colspec += " NOT NULL"
        return colspec

    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 " % preparer.quote(using)

        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
            elements.append(
                "%s WITH %s" % (self.sql_compiler.process(expr, **kw), op)
            )
        text += "EXCLUDE USING %s (%s)" % (
            constraint.using,
            ", ".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)


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_, **kw):
        return self.dialect.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:`.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)
        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")
        )
        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
            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
        """
        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,
        ) in rows:
            column_info = self._get_column_info(
                name,
                format_type,
                default_,
                notnull,
                domains,
                enums,
                schema,
                comment,
            )
            columns.append(column_info)
        return columns

    def _get_column_info(
        self,
        name,
        format_type,
        default,
        notnull,
        domains,
        enums,
        schema,
        comment,
    ):
        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
        # 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,
        )
        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, am.amname
              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 "",
                "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,
                  i.reloptions, am.amname
              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')
                  and t.oid = :table_oid
                  and ix.indisprimary = 'f'
              ORDER BY
                  t.relname,
                  i.relname
            """

        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,
                options,
                amname,
            ) = 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:
                index["key"] = [int(k.strip()) for k in idx_key.split()]
                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 "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)

        # samples:
        # "CHECK (((a > 1) AND (a < 5)))"
        # "CHECK (((a = 1) OR ((a > 2) AND (a < 5))))"
        def match_cons(src):
            m = re.match(r"^CHECK *\(\((.+)\)\)$", src)
            if not m:
                util.warn("Could not parse CHECK constraint text: %r" % src)
                return ""
            return m.group(1)

        return [
            {"name": name, "sqltext": match_cons(src)}
            for name, src in c.fetchall()
        ]

    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": [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
