text: # oracle/base.py
  # Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
  # <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: https://www.opensource.org/licenses/mit-license.php
  
  r"""
  .. dialect:: oracle
      :name: Oracle
      :full_support: 11.2, 18c
      :normal_support: 11+
      :best_effort: 9+
  
  
  Auto Increment Behavior
  -----------------------
  
  SQLAlchemy Table objects which include integer primary keys are usually
  assumed to have "autoincrementing" behavior, meaning they can generate their
  own primary key values upon INSERT. For use within Oracle, two options are
  available, which are the use of IDENTITY columns (Oracle 12 and above only)
  or the association of a SEQUENCE with the column.
  
  Specifying GENERATED AS IDENTITY (Oracle 12 and above)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  Starting from version 12 Oracle can make use of identity columns using
  the :class:`_sql.Identity` to specify the autoincrementing behavior::
  
      t = Table('mytable', metadata,
          Column('id', Integer, Identity(start=3), primary_key=True),
          Column(...), ...
      )
  
  The CREATE TABLE for the above :class:`_schema.Table` object would be:
  
  .. sourcecode:: sql
  
      CREATE TABLE mytable (
          id INTEGER GENERATED BY DEFAULT AS IDENTITY (START WITH 3),
          ...,
          PRIMARY KEY (id)
      )
  
  The :class:`_schema.Identity` object support many options to control the
  "autoincrementing" behavior of the column, like the starting value, the
  incrementing value, etc.
  In addition to the standard options, Oracle supports setting
  :paramref:`_schema.Identity.always` to ``None`` to use the default
  generated mode, rendering GENERATED AS IDENTITY in the DDL. It also supports
  setting :paramref:`_schema.Identity.on_null` to ``True`` to specify ON NULL
  in conjunction with a 'BY DEFAULT' identity column.
  
  Using a SEQUENCE (all Oracle versions)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  Older version of Oracle had no "autoincrement"
  feature, SQLAlchemy relies upon sequences to produce these values.   With the
  older Oracle versions, *a sequence must always be explicitly specified to
  enable autoincrement*.  This is divergent with the majority of documentation
  examples which assume the usage of an autoincrement-capable database.   To
  specify sequences, use the sqlalchemy.schema.Sequence object which is passed
  to a Column construct::
  
    t = Table('mytable', metadata,
          Column('id', Integer, Sequence('id_seq'), primary_key=True),
          Column(...), ...
    )
  
  This step is also required when using table reflection, i.e. autoload_with=engine::
  
    t = Table('mytable', metadata,
          Column('id', Integer, Sequence('id_seq'), primary_key=True),
          autoload_with=engine
    )
  
  .. versionchanged::  1.4   Added :class:`_schema.Identity` construct
     in a :class:`_schema.Column` to specify the option of an autoincrementing
     column.
  
  .. _oracle_isolation_level:
  
  Transaction Isolation Level / Autocommit
  ----------------------------------------
  
  The Oracle database supports "READ COMMITTED" and "SERIALIZABLE" modes of
  isolation. The AUTOCOMMIT isolation level is also supported by the cx_Oracle
  dialect.
  
  To set using per-connection execution options::
  
      connection = engine.connect()
      connection = connection.execution_options(
          isolation_level="AUTOCOMMIT"
      )
  
  For ``READ COMMITTED`` and ``SERIALIZABLE``, the Oracle dialect sets the
  level at the session level using ``ALTER SESSION``, which is reverted back
  to its default setting when the connection is returned to the connection
  pool.
  
  Valid values for ``isolation_level`` include:
  
  * ``READ COMMITTED``
  * ``AUTOCOMMIT``
  * ``SERIALIZABLE``
  
  .. note:: The implementation for the
     :meth:`_engine.Connection.get_isolation_level` method as implemented by the
     Oracle dialect necessarily forces the start of a transaction using the
     Oracle LOCAL_TRANSACTION_ID function; otherwise no level is normally
     readable.
  
     Additionally, the :meth:`_engine.Connection.get_isolation_level` method will
     raise an exception if the ``v$transaction`` view is not available due to
     permissions or other reasons, which is a common occurrence in Oracle
     installations.
  
     The cx_Oracle dialect attempts to call the
     :meth:`_engine.Connection.get_isolation_level` method when the dialect makes
     its first connection to the database in order to acquire the
     "default"isolation level.  This default level is necessary so that the level
     can be reset on a connection after it has been temporarily modified using
     :meth:`_engine.Connection.execution_options` method.   In the common event
     that the :meth:`_engine.Connection.get_isolation_level` method raises an
     exception due to ``v$transaction`` not being readable as well as any other
     database-related failure, the level is assumed to be "READ COMMITTED".  No
     warning is emitted for this initial first-connect condition as it is
     expected to be a common restriction on Oracle databases.
  
  .. versionadded:: 1.3.16 added support for AUTOCOMMIT to the cx_oracle dialect
     as well as the notion of a default isolation level
  
  .. versionadded:: 1.3.21 Added support for SERIALIZABLE as well as live
     reading of the isolation level.
  
  .. versionchanged:: 1.3.22 In the event that the default isolation
     level cannot be read due to permissions on the v$transaction view as
     is common in Oracle installations, the default isolation level is hardcoded
     to "READ COMMITTED" which was the behavior prior to 1.3.21.
  
  .. seealso::
  
      :ref:`dbapi_autocommit`
  
  Identifier Casing
  -----------------
  
  In Oracle, the data dictionary represents all case insensitive identifier
  names using UPPERCASE text.   SQLAlchemy on the other hand considers an
  all-lower case identifier name to be case insensitive.   The Oracle dialect
  converts all case insensitive identifiers to and from those two formats during
  schema level communication, such as reflection of tables and indexes.   Using
  an UPPERCASE name on the SQLAlchemy side indicates a case sensitive
  identifier, and SQLAlchemy will quote the name - this will cause mismatches
  against data dictionary data received from Oracle, so unless identifier names
  have been truly created as case sensitive (i.e. using quoted names), all
  lowercase names should be used on the SQLAlchemy side.
  
  .. _oracle_max_identifier_lengths:
  
  Max Identifier Lengths
  ----------------------
  
  Oracle has changed the default max identifier length as of Oracle Server
  version 12.2.   Prior to this version, the length was 30, and for 12.2 and
  greater it is now 128.   This change impacts SQLAlchemy in the area of
  generated SQL label names as well as the generation of constraint names,
  particularly in the case where the constraint naming convention feature
  described at :ref:`constraint_naming_conventions` is being used.
  
  To assist with this change and others, Oracle includes the concept of a
  "compatibility" version, which is a version number that is independent of the
  actual server version in order to assist with migration of Oracle databases,
  and may be configured within the Oracle server itself. This compatibility
  version is retrieved using the query  ``SELECT value FROM v$parameter WHERE
  name = 'compatible';``.   The SQLAlchemy Oracle dialect, when tasked with
  determining the default max identifier length, will attempt to use this query
  upon first connect in order to determine the effective compatibility version of
  the server, which determines what the maximum allowed identifier length is for
  the server.  If the table is not available, the  server version information is
  used instead.
  
  As of SQLAlchemy 1.4, the default max identifier length for the Oracle dialect
  is 128 characters.  Upon first connect, the compatibility version is detected
  and if it is less than Oracle version 12.2, the max identifier length is
  changed to be 30 characters.  In all cases, setting the
  :paramref:`_sa.create_engine.max_identifier_length` parameter will bypass this
  change and the value given will be used as is::
  
      engine = create_engine(
          "oracle+cx_oracle://scott:tiger@oracle122",
          max_identifier_length=30)
  
  The maximum identifier length comes into play both when generating anonymized
  SQL labels in SELECT statements, but more crucially when generating constraint
  names from a naming convention.  It is this area that has created the need for
  SQLAlchemy to change this default conservatively.   For example, the following
  naming convention produces two very different constraint names based on the
  identifier length::
  
      from sqlalchemy import Column
      from sqlalchemy import Index
      from sqlalchemy import Integer
      from sqlalchemy import MetaData
      from sqlalchemy import Table
      from sqlalchemy.dialects import oracle
      from sqlalchemy.schema import CreateIndex
  
      m = MetaData(naming_convention={"ix": "ix_%(column_0N_name)s"})
  
      t = Table(
          "t",
          m,
          Column("some_column_name_1", Integer),
          Column("some_column_name_2", Integer),
          Column("some_column_name_3", Integer),
      )
  
      ix = Index(
          None,
          t.c.some_column_name_1,
          t.c.some_column_name_2,
          t.c.some_column_name_3,
      )
  
      oracle_dialect = oracle.dialect(max_identifier_length=30)
      print(CreateIndex(ix).compile(dialect=oracle_dialect))
  
  With an identifier length of 30, the above CREATE INDEX looks like::
  
      CREATE INDEX ix_some_column_name_1s_70cd ON t
      (some_column_name_1, some_column_name_2, some_column_name_3)
  
  However with length=128, it becomes::
  
      CREATE INDEX ix_some_column_name_1some_column_name_2some_column_name_3 ON t
      (some_column_name_1, some_column_name_2, some_column_name_3)
  
  Applications which have run versions of SQLAlchemy prior to 1.4 on an  Oracle
  server version 12.2 or greater are therefore subject to the scenario of a
  database migration that wishes to "DROP CONSTRAINT" on a name that was
  previously generated with the shorter length.  This migration will fail when
  the identifier length is changed without the name of the index or constraint
  first being adjusted.  Such applications are strongly advised to make use of
  :paramref:`_sa.create_engine.max_identifier_length`
  in order to maintain control
  of the generation of truncated names, and to fully review and test all database
  migrations in a staging environment when changing this value to ensure that the
  impact of this change has been mitigated.
  
  .. versionchanged:: 1.4 the default max_identifier_length for Oracle is 128
     characters, which is adjusted down to 30 upon first connect if an older
     version of Oracle server (compatibility version < 12.2) is detected.
  
  
  LIMIT/OFFSET Support
  --------------------
  
  Oracle has no direct support for LIMIT and OFFSET until version 12c.
  To achieve this behavior across all widely used versions of Oracle starting
  with the 8 series, SQLAlchemy currently makes use of ROWNUM to achieve
  LIMIT/OFFSET; the exact methodology is taken from
  https://blogs.oracle.com/oraclemagazine/on-rownum-and-limiting-results .
  
  There is currently a single option to affect its behavior:
  
  * the "FIRST_ROWS()" optimization keyword is not used by default.  To enable
    the usage of this optimization directive, specify ``optimize_limits=True``
    to :func:`_sa.create_engine`.
  
  .. versionchanged:: 1.4
      The Oracle dialect renders limit/offset integer values using a "post
      compile" scheme which renders the integer directly before passing the
      statement to the cursor for execution.   The ``use_binds_for_limits`` flag
      no longer has an effect.
  
      .. seealso::
  
          :ref:`change_4808`.
  
  Support for changing the row number strategy, which would include one that
  makes use of the ``row_number()`` window function as well as one that makes
  use of the Oracle 12c  "FETCH FIRST N ROW / OFFSET N ROWS" keywords may be
  added in a future release.
  
  
  .. _oracle_returning:
  
  RETURNING Support
  -----------------
  
  The Oracle database supports a limited form of RETURNING, in order to retrieve
  result sets of matched rows from INSERT, UPDATE and DELETE statements.
  Oracle's RETURNING..INTO syntax only supports one row being returned, as it
  relies upon OUT parameters in order to function.  In addition, supported
  DBAPIs have further limitations (see :ref:`cx_oracle_returning`).
  
  SQLAlchemy's "implicit returning" feature, which employs RETURNING within an
  INSERT and sometimes an UPDATE statement in order to fetch newly generated
  primary key values and other SQL defaults and expressions, is normally enabled
  on the Oracle backend.  By default, "implicit returning" typically only
  fetches the value of a single ``nextval(some_seq)`` expression embedded into
  an INSERT in order to increment a sequence within an INSERT statement and get
  the value back at the same time. To disable this feature across the board,
  specify ``implicit_returning=False`` to :func:`_sa.create_engine`::
  
      engine = create_engine("oracle+cx_oracle://scott:tiger@dsn",
                             implicit_returning=False)
  
  Implicit returning can also be disabled on a table-by-table basis as a table
  option::
  
      # Core Table
      my_table = Table("my_table", metadata, ..., implicit_returning=False)
  
  
      # declarative
      class MyClass(Base):
          __tablename__ = 'my_table'
          __table_args__ = {"implicit_returning": False}
  
  .. seealso::
  
      :ref:`cx_oracle_returning` - additional cx_oracle-specific restrictions on
      implicit returning.
  
  ON UPDATE CASCADE
  -----------------
  
  Oracle doesn't have native ON UPDATE CASCADE functionality.  A trigger based
  solution is available at
  https://asktom.oracle.com/tkyte/update_cascade/index.html .
  
  When using the SQLAlchemy ORM, the ORM has limited ability to manually issue
  cascading updates - specify ForeignKey objects using the
  "deferrable=True, initially='deferred'" keyword arguments,
  and specify "passive_updates=False" on each relationship().
  
  Oracle 8 Compatibility
  ----------------------
  
  .. warning:: The status of Oracle 8 compatibility is not known for SQLAlchemy
     2.0.
  
  When Oracle 8 is detected, the dialect internally configures itself to the
  following behaviors:
  
  * the use_ansi flag is set to False.  This has the effect of converting all
    JOIN phrases into the WHERE clause, and in the case of LEFT OUTER JOIN
    makes use of Oracle's (+) operator.
  
  * the NVARCHAR2 and NCLOB datatypes are no longer generated as DDL when
    the :class:`~sqlalchemy.types.Unicode` is used - VARCHAR2 and CLOB are issued
    instead. This because these types don't seem to work correctly on Oracle 8
    even though they are available. The :class:`~sqlalchemy.types.NVARCHAR` and
    :class:`~sqlalchemy.dialects.oracle.NCLOB` types will always generate
    NVARCHAR2 and NCLOB.
  
  
  Synonym/DBLINK Reflection
  -------------------------
  
  When using reflection with Table objects, the dialect can optionally search
  for tables indicated by synonyms, either in local or remote schemas or
  accessed over DBLINK, by passing the flag ``oracle_resolve_synonyms=True`` as
  a keyword argument to the :class:`_schema.Table` construct::
  
      some_table = Table('some_table', autoload_with=some_engine,
                                  oracle_resolve_synonyms=True)
  
  When this flag is set, the given name (such as ``some_table`` above) will
  be searched not just in the ``ALL_TABLES`` view, but also within the
  ``ALL_SYNONYMS`` view to see if this name is actually a synonym to another
  name.  If the synonym is located and refers to a DBLINK, the oracle dialect
  knows how to locate the table's information using DBLINK syntax(e.g.
  ``@dblink``).
  
  ``oracle_resolve_synonyms`` is accepted wherever reflection arguments are
  accepted, including methods such as :meth:`_schema.MetaData.reflect` and
  :meth:`_reflection.Inspector.get_columns`.
  
  If synonyms are not in use, this flag should be left disabled.
  
  .. _oracle_constraint_reflection:
  
  Constraint Reflection
  ---------------------
  
  The Oracle dialect can return information about foreign key, unique, and
  CHECK constraints, as well as indexes on tables.
  
  Raw information regarding these constraints can be acquired using
  :meth:`_reflection.Inspector.get_foreign_keys`,
  :meth:`_reflection.Inspector.get_unique_constraints`,
  :meth:`_reflection.Inspector.get_check_constraints`, and
  :meth:`_reflection.Inspector.get_indexes`.
  
  .. versionchanged:: 1.2  The Oracle dialect can now reflect UNIQUE and
     CHECK constraints.
  
  When using reflection at the :class:`_schema.Table` level, the
  :class:`_schema.Table`
  will also include these constraints.
  
  Note the following caveats:
  
  * When using the :meth:`_reflection.Inspector.get_check_constraints` method,
    Oracle
    builds a special "IS NOT NULL" constraint for columns that specify
    "NOT NULL".  This constraint is **not** returned by default; to include
    the "IS NOT NULL" constraints, pass the flag ``include_all=True``::
  
        from sqlalchemy import create_engine, inspect
  
        engine = create_engine("oracle+cx_oracle://s:t@dsn")
        inspector = inspect(engine)
        all_check_constraints = inspector.get_check_constraints(
            "some_table", include_all=True)
  
  * in most cases, when reflecting a :class:`_schema.Table`,
    a UNIQUE constraint will
    **not** be available as a :class:`.UniqueConstraint` object, as Oracle
    mirrors unique constraints with a UNIQUE index in most cases (the exception
    seems to be when two or more unique constraints represent the same columns);
    the :class:`_schema.Table` will instead represent these using
    :class:`.Index`
    with the ``unique=True`` flag set.
  
  * Oracle creates an implicit index for the primary key of a table; this index
    is **excluded** from all index results.
  
  * the list of columns reflected for an index will not include column names
    that start with SYS_NC.
  
  Table names with SYSTEM/SYSAUX tablespaces
  -------------------------------------------
  
  The :meth:`_reflection.Inspector.get_table_names` and
  :meth:`_reflection.Inspector.get_temp_table_names`
  methods each return a list of table names for the current engine. These methods
  are also part of the reflection which occurs within an operation such as
  :meth:`_schema.MetaData.reflect`.  By default,
  these operations exclude the ``SYSTEM``
  and ``SYSAUX`` tablespaces from the operation.   In order to change this, the
  default list of tablespaces excluded can be changed at the engine level using
  the ``exclude_tablespaces`` parameter::
  
      # exclude SYSAUX and SOME_TABLESPACE, but not SYSTEM
      e = create_engine(
        "oracle+cx_oracle://scott:tiger@xe",
        exclude_tablespaces=["SYSAUX", "SOME_TABLESPACE"])
  
  .. versionadded:: 1.1
  
  DateTime Compatibility
  ----------------------
  
  Oracle has no datatype known as ``DATETIME``, it instead has only ``DATE``,
  which can actually store a date and time value.  For this reason, the Oracle
  dialect provides a type :class:`_oracle.DATE` which is a subclass of
  :class:`.DateTime`.   This type has no special behavior, and is only
  present as a "marker" for this type; additionally, when a database column
  is reflected and the type is reported as ``DATE``, the time-supporting
  :class:`_oracle.DATE` type is used.
  
  .. versionchanged:: 0.9.4 Added :class:`_oracle.DATE` to subclass
     :class:`.DateTime`.  This is a change as previous versions
     would reflect a ``DATE`` column as :class:`_types.DATE`, which subclasses
     :class:`.Date`.   The only significance here is for schemes that are
     examining the type of column for use in special Python translations or
     for migrating schemas to other database backends.
  
  .. _oracle_table_options:
  
  Oracle Table Options
  -------------------------
  
  The CREATE TABLE phrase supports the following options with Oracle
  in conjunction with the :class:`_schema.Table` construct:
  
  
  * ``ON COMMIT``::
  
      Table(
          "some_table", metadata, ...,
          prefixes=['GLOBAL TEMPORARY'], oracle_on_commit='PRESERVE ROWS')
  
  .. versionadded:: 1.0.0
  
  * ``COMPRESS``::
  
      Table('mytable', metadata, Column('data', String(32)),
          oracle_compress=True)
  
      Table('mytable', metadata, Column('data', String(32)),
          oracle_compress=6)
  
     The ``oracle_compress`` parameter accepts either an integer compression
     level, or ``True`` to use the default compression level.
  
  .. versionadded:: 1.0.0
  
  .. _oracle_index_options:
  
  Oracle Specific Index Options
  -----------------------------
  
  Bitmap Indexes
  ~~~~~~~~~~~~~~
  
  You can specify the ``oracle_bitmap`` parameter to create a bitmap index
  instead of a B-tree index::
  
      Index('my_index', my_table.c.data, oracle_bitmap=True)
  
  Bitmap indexes cannot be unique and cannot be compressed. SQLAlchemy will not
  check for such limitations, only the database will.
  
  .. versionadded:: 1.0.0
  
  Index compression
  ~~~~~~~~~~~~~~~~~
  
  Oracle has a more efficient storage mode for indexes containing lots of
  repeated values. Use the ``oracle_compress`` parameter to turn on key
  compression::
  
      Index('my_index', my_table.c.data, oracle_compress=True)
  
      Index('my_index', my_table.c.data1, my_table.c.data2, unique=True,
             oracle_compress=1)
  
  The ``oracle_compress`` parameter accepts either an integer specifying the
  number of prefix columns to compress, or ``True`` to use the default (all
  columns for non-unique indexes, all but the last column for unique indexes).
  
  .. versionadded:: 1.0.0
  
  """  # noqa
  
  from itertools import groupby
  import re
  
  from ... import Computed
  from ... import exc
  from ... import schema as sa_schema
  from ... import sql
  from ... import util
  from ...engine import default
  from ...engine import reflection
  from ...sql import compiler
  from ...sql import expression
  from ...sql import sqltypes
  from ...sql import util as sql_util
  from ...sql import visitors
  from ...types import BLOB
  from ...types import CHAR
  from ...types import CLOB
  from ...types import FLOAT
  from ...types import INTEGER
  from ...types import NCHAR
  from ...types import NVARCHAR
  from ...types import TIMESTAMP
  from ...types import VARCHAR
  
  RESERVED_WORDS = set(
      "SHARE RAW DROP BETWEEN FROM DESC OPTION PRIOR LONG THEN "
      "DEFAULT ALTER IS INTO MINUS INTEGER NUMBER GRANT IDENTIFIED "
      "ALL TO ORDER ON FLOAT DATE HAVING CLUSTER NOWAIT RESOURCE "
      "ANY TABLE INDEX FOR UPDATE WHERE CHECK SMALLINT WITH DELETE "
      "BY ASC REVOKE LIKE SIZE RENAME NOCOMPRESS NULL GROUP VALUES "
      "AS IN VIEW EXCLUSIVE COMPRESS SYNONYM SELECT INSERT EXISTS "
      "NOT TRIGGER ELSE CREATE INTERSECT PCTFREE DISTINCT USER "
      "CONNECT SET MODE OF UNIQUE VARCHAR2 VARCHAR LOCK OR CHAR "
      "DECIMAL UNION PUBLIC AND START UID COMMENT CURRENT LEVEL".split()
  )
  
  NO_ARG_FNS = set(
      "UID CURRENT_DATE SYSDATE USER " "CURRENT_TIME CURRENT_TIMESTAMP".split()
  )
  
  
  class RAW(sqltypes._Binary):
      __visit_name__ = "RAW"
  
  
  OracleRaw = RAW
  
  
  class NCLOB(sqltypes.Text):
      __visit_name__ = "NCLOB"
  
  
  class VARCHAR2(VARCHAR):
      __visit_name__ = "VARCHAR2"
  
  
  NVARCHAR2 = NVARCHAR
  
  
  class NUMBER(sqltypes.Numeric, sqltypes.Integer):
      __visit_name__ = "NUMBER"
  
      def __init__(self, precision=None, scale=None, asdecimal=None):
          if asdecimal is None:
              asdecimal = bool(scale and scale > 0)
  
          super(NUMBER, self).__init__(
              precision=precision, scale=scale, asdecimal=asdecimal
          )
  
      def adapt(self, impltype):
          ret = super(NUMBER, self).adapt(impltype)
          # leave a hint for the DBAPI handler
          ret._is_oracle_number = True
          return ret
  
      @property
      def _type_affinity(self):
          if bool(self.scale and self.scale > 0):
              return sqltypes.Numeric
          else:
              return sqltypes.Integer
  
  
  class DOUBLE_PRECISION(sqltypes.Float):
      __visit_name__ = "DOUBLE_PRECISION"
  
  
  class BINARY_DOUBLE(sqltypes.Float):
      __visit_name__ = "BINARY_DOUBLE"
  
  
  class BINARY_FLOAT(sqltypes.Float):
      __visit_name__ = "BINARY_FLOAT"
  
  
  class BFILE(sqltypes.LargeBinary):
      __visit_name__ = "BFILE"
  
  
  class LONG(sqltypes.Text):
      __visit_name__ = "LONG"
  
  
  class DATE(sqltypes.DateTime):
      """Provide the oracle DATE type.
  
      This type has no special Python behavior, except that it subclasses
      :class:`_types.DateTime`; this is to suit the fact that the Oracle
      ``DATE`` type supports a time value.
  
      .. versionadded:: 0.9.4
  
      """
  
      __visit_name__ = "DATE"
  
      def _compare_type_affinity(self, other):
          return other._type_affinity in (sqltypes.DateTime, sqltypes.Date)
  
  
  class INTERVAL(sqltypes.NativeForEmulated, sqltypes._AbstractInterval):
      __visit_name__ = "INTERVAL"
  
      def __init__(self, day_precision=None, second_precision=None):
          """Construct an INTERVAL.
  
          Note that only DAY TO SECOND intervals are currently supported.
          This is due to a lack of support for YEAR TO MONTH intervals
          within available DBAPIs.
  
          :param day_precision: the day precision value.  this is the number of
            digits to store for the day field.  Defaults to "2"
          :param second_precision: the second precision value.  this is the
            number of digits to store for the fractional seconds field.
            Defaults to "6".
  
          """
          self.day_precision = day_precision
          self.second_precision = second_precision
  
      @classmethod
      def _adapt_from_generic_interval(cls, interval):
          return INTERVAL(
              day_precision=interval.day_precision,
              second_precision=interval.second_precision,
          )
  
      @property
      def _type_affinity(self):
          return sqltypes.Interval
  
      def as_generic(self, allow_nulltype=False):
          return sqltypes.Interval(
              native=True,
              second_precision=self.second_precision,
              day_precision=self.day_precision,
          )
  
      def coerce_compared_value(self, op, value):
          return self
  
  
  class ROWID(sqltypes.TypeEngine):
      """Oracle ROWID type.
  
      When used in a cast() or similar, generates ROWID.
  
      """
  
      __visit_name__ = "ROWID"
  
  
  class _OracleBoolean(sqltypes.Boolean):
      def get_dbapi_type(self, dbapi):
          return dbapi.NUMBER
  
  
  colspecs = {
      sqltypes.Boolean: _OracleBoolean,
      sqltypes.Interval: INTERVAL,
      sqltypes.DateTime: DATE,
  }
  
  ischema_names = {
      "VARCHAR2": VARCHAR,
      "NVARCHAR2": NVARCHAR,
      "CHAR": CHAR,
      "NCHAR": NCHAR,
      "DATE": DATE,
      "NUMBER": NUMBER,
      "BLOB": BLOB,
      "BFILE": BFILE,
      "CLOB": CLOB,
      "NCLOB": NCLOB,
      "TIMESTAMP": TIMESTAMP,
      "TIMESTAMP WITH TIME ZONE": TIMESTAMP,
      "INTERVAL DAY TO SECOND": INTERVAL,
      "RAW": RAW,
      "FLOAT": FLOAT,
      "DOUBLE PRECISION": DOUBLE_PRECISION,
      "LONG": LONG,
      "BINARY_DOUBLE": BINARY_DOUBLE,
      "BINARY_FLOAT": BINARY_FLOAT,
  }
  
  
  class OracleTypeCompiler(compiler.GenericTypeCompiler):
      # Note:
      # Oracle DATE == DATETIME
      # Oracle does not allow milliseconds in DATE
      # Oracle does not support TIME columns
  
      def visit_datetime(self, type_, **kw):
          return self.visit_DATE(type_, **kw)
  
      def visit_float(self, type_, **kw):
          return self.visit_FLOAT(type_, **kw)
  
      def visit_unicode(self, type_, **kw):
          if self.dialect._use_nchar_for_unicode:
              return self.visit_NVARCHAR2(type_, **kw)
          else:
              return self.visit_VARCHAR2(type_, **kw)
  
      def visit_INTERVAL(self, type_, **kw):
          return "INTERVAL DAY%s TO SECOND%s" % (
              type_.day_precision is not None
              and "(%d)" % type_.day_precision
              or "",
              type_.second_precision is not None
              and "(%d)" % type_.second_precision
              or "",
          )
  
      def visit_LONG(self, type_, **kw):
          return "LONG"
  
      def visit_TIMESTAMP(self, type_, **kw):
          if type_.timezone:
              return "TIMESTAMP WITH TIME ZONE"
          else:
              return "TIMESTAMP"
  
      def visit_DOUBLE_PRECISION(self, type_, **kw):
          return self._generate_numeric(type_, "DOUBLE PRECISION", **kw)
  
      def visit_BINARY_DOUBLE(self, type_, **kw):
          return self._generate_numeric(type_, "BINARY_DOUBLE", **kw)
  
      def visit_BINARY_FLOAT(self, type_, **kw):
          return self._generate_numeric(type_, "BINARY_FLOAT", **kw)
  
      def visit_FLOAT(self, type_, **kw):
          # don't support conversion between decimal/binary
          # precision yet
          kw["no_precision"] = True
          return self._generate_numeric(type_, "FLOAT", **kw)
  
      def visit_NUMBER(self, type_, **kw):
          return self._generate_numeric(type_, "NUMBER", **kw)
  
      def _generate_numeric(
          self, type_, name, precision=None, scale=None, no_precision=False, **kw
      ):
          if precision is None:
              precision = type_.precision
  
          if scale is None:
              scale = getattr(type_, "scale", None)
  
          if no_precision or precision is None:
              return name
          elif scale is None:
              n = "%(name)s(%(precision)s)"
              return n % {"name": name, "precision": precision}
          else:
              n = "%(name)s(%(precision)s, %(scale)s)"
              return n % {"name": name, "precision": precision, "scale": scale}
  
      def visit_string(self, type_, **kw):
          return self.visit_VARCHAR2(type_, **kw)
  
      def visit_VARCHAR2(self, type_, **kw):
          return self._visit_varchar(type_, "", "2")
  
      def visit_NVARCHAR2(self, type_, **kw):
          return self._visit_varchar(type_, "N", "2")
  
      visit_NVARCHAR = visit_NVARCHAR2
  
      def visit_VARCHAR(self, type_, **kw):
          return self._visit_varchar(type_, "", "")
  
      def _visit_varchar(self, type_, n, num):
          if not type_.length:
              return "%(n)sVARCHAR%(two)s" % {"two": num, "n": n}
          elif not n and self.dialect._supports_char_length:
              varchar = "VARCHAR%(two)s(%(length)s CHAR)"
              return varchar % {"length": type_.length, "two": num}
          else:
              varchar = "%(n)sVARCHAR%(two)s(%(length)s)"
              return varchar % {"length": type_.length, "two": num, "n": n}
  
      def visit_text(self, type_, **kw):
          return self.visit_CLOB(type_, **kw)
  
      def visit_unicode_text(self, type_, **kw):
          if self.dialect._use_nchar_for_unicode:
              return self.visit_NCLOB(type_, **kw)
          else:
              return self.visit_CLOB(type_, **kw)
  
      def visit_large_binary(self, type_, **kw):
          return self.visit_BLOB(type_, **kw)
  
      def visit_big_integer(self, type_, **kw):
          return self.visit_NUMBER(type_, precision=19, **kw)
  
      def visit_boolean(self, type_, **kw):
          return self.visit_SMALLINT(type_, **kw)
  
      def visit_RAW(self, type_, **kw):
          if type_.length:
              return "RAW(%(length)s)" % {"length": type_.length}
          else:
              return "RAW"
  
      def visit_ROWID(self, type_, **kw):
          return "ROWID"
  
  
  class OracleCompiler(compiler.SQLCompiler):
      """Oracle compiler modifies the lexical structure of Select
      statements to work under non-ANSI configured Oracle databases, if
      the use_ansi flag is False.
      """
  
      compound_keywords = util.update_copy(
          compiler.SQLCompiler.compound_keywords,
          {expression.CompoundSelect.EXCEPT: "MINUS"},
      )
  
      def __init__(self, *args, **kwargs):
          self.__wheres = {}
          super(OracleCompiler, self).__init__(*args, **kwargs)
  
      def visit_mod_binary(self, binary, operator, **kw):
          return "mod(%s, %s)" % (
              self.process(binary.left, **kw),
              self.process(binary.right, **kw),
          )
  
      def visit_now_func(self, fn, **kw):
          return "CURRENT_TIMESTAMP"
  
      def visit_char_length_func(self, fn, **kw):
          return "LENGTH" + self.function_argspec(fn, **kw)
  
      def visit_match_op_binary(self, binary, operator, **kw):
          return "CONTAINS (%s, %s)" % (
              self.process(binary.left),
              self.process(binary.right),
          )
  
      def visit_true(self, expr, **kw):
          return "1"
  
      def visit_false(self, expr, **kw):
          return "0"
  
      def get_cte_preamble(self, recursive):
          return "WITH"
  
      def get_select_hint_text(self, byfroms):
          return " ".join("/*+ %s */" % text for table, text in byfroms.items())
  
      def function_argspec(self, fn, **kw):
          if len(fn.clauses) > 0 or fn.name.upper() not in NO_ARG_FNS:
              return compiler.SQLCompiler.function_argspec(self, fn, **kw)
          else:
              return ""
  
      def visit_function(self, func, **kw):
          text = super(OracleCompiler, self).visit_function(func, **kw)
          if kw.get("asfrom", False):
              text = "TABLE (%s)" % func
          return text
  
      def visit_table_valued_column(self, element, **kw):
          text = super(OracleCompiler, self).visit_table_valued_column(
              element, **kw
          )
          text = "COLUMN_VALUE " + text
          return text
  
      def default_from(self):
          """Called when a ``SELECT`` statement has no froms,
          and no ``FROM`` clause is to be appended.
  
          The Oracle compiler tacks a "FROM DUAL" to the statement.
          """
  
          return " FROM DUAL"
  
      def visit_join(self, join, from_linter=None, **kwargs):
          if self.dialect.use_ansi:
              return compiler.SQLCompiler.visit_join(
                  self, join, from_linter=from_linter, **kwargs
              )
          else:
              if from_linter:
                  from_linter.edges.add((join.left, join.right))
  
              kwargs["asfrom"] = True
              if isinstance(join.right, expression.FromGrouping):
                  right = join.right.element
              else:
                  right = join.right
              return (
                  self.process(join.left, from_linter=from_linter, **kwargs)
                  + ", "
                  + self.process(right, from_linter=from_linter, **kwargs)
              )
  
      def _get_nonansi_join_whereclause(self, froms):
          clauses = []
  
          def visit_join(join):
              if join.isouter:
                  # https://docs.oracle.com/database/121/SQLRF/queries006.htm#SQLRF52354
                  # "apply the outer join operator (+) to all columns of B in
                  # the join condition in the WHERE clause" - that is,
                  # unconditionally regardless of operator or the other side
                  def visit_binary(binary):
                      if isinstance(
                          binary.left, expression.ColumnClause
                      ) and join.right.is_derived_from(binary.left.table):
                          binary.left = _OuterJoinColumn(binary.left)
                      elif isinstance(
                          binary.right, expression.ColumnClause
                      ) and join.right.is_derived_from(binary.right.table):
                          binary.right = _OuterJoinColumn(binary.right)
  
                  clauses.append(
                      visitors.cloned_traverse(
                          join.onclause, {}, {"binary": visit_binary}
                      )
                  )
              else:
                  clauses.append(join.onclause)
  
              for j in join.left, join.right:
                  if isinstance(j, expression.Join):
                      visit_join(j)
                  elif isinstance(j, expression.FromGrouping):
                      visit_join(j.element)
  
          for f in froms:
              if isinstance(f, expression.Join):
                  visit_join(f)
  
          if not clauses:
              return None
          else:
              return sql.and_(*clauses)
  
      def visit_outer_join_column(self, vc, **kw):
          return self.process(vc.column, **kw) + "(+)"
  
      def visit_sequence(self, seq, **kw):
          return self.preparer.format_sequence(seq) + ".nextval"
  
      def get_render_as_alias_suffix(self, alias_name_text):
          """Oracle doesn't like ``FROM table AS alias``"""
  
          return " " + alias_name_text
  
      def returning_clause(self, stmt, returning_cols):
          columns = []
          binds = []
  
          for i, column in enumerate(
              expression._select_iterables(returning_cols)
          ):
              if (
                  self.isupdate
                  and isinstance(column, sa_schema.Column)
                  and isinstance(column.server_default, Computed)
                  and not self.dialect._supports_update_returning_computed_cols
              ):
                  util.warn(
                      "Computed columns don't work with Oracle UPDATE "
                      "statements that use RETURNING; the value of the column "
                      "*before* the UPDATE takes place is returned.   It is "
                      "advised to not use RETURNING with an Oracle computed "
                      "column.  Consider setting implicit_returning to False on "
                      "the Table object in order to avoid implicit RETURNING "
                      "clauses from being generated for this Table."
                  )
              if column.type._has_column_expression:
                  col_expr = column.type.column_expression(column)
              else:
                  col_expr = column
  
              outparam = sql.outparam("ret_%d" % i, type_=column.type)
              self.binds[outparam.key] = outparam
              binds.append(
                  self.bindparam_string(self._truncate_bindparam(outparam))
              )
  
              # ensure the ExecutionContext.get_out_parameters() method is
              # *not* called; the cx_Oracle dialect wants to handle these
              # parameters separately
              self.has_out_parameters = False
  
              columns.append(self.process(col_expr, within_columns_clause=False))
  
              self._add_to_result_map(
                  getattr(col_expr, "name", col_expr._anon_name_label),
                  getattr(col_expr, "name", col_expr._anon_name_label),
                  (
                      column,
                      getattr(column, "name", None),
                      getattr(column, "key", None),
                  ),
                  column.type,
              )
  
          return "RETURNING " + ", ".join(columns) + " INTO " + ", ".join(binds)
  
      def translate_select_structure(self, select_stmt, **kwargs):
          select = select_stmt
  
          if not getattr(select, "_oracle_visit", None):
              if not self.dialect.use_ansi:
                  froms = self._display_froms_for_select(
                      select, kwargs.get("asfrom", False)
                  )
                  whereclause = self._get_nonansi_join_whereclause(froms)
                  if whereclause is not None:
                      select = select.where(whereclause)
                      select._oracle_visit = True
  
              # if fetch is used this is not needed
              if (
                  select._has_row_limiting_clause
                  and select._fetch_clause is None
              ):
                  limit_clause = select._limit_clause
                  offset_clause = select._offset_clause
  
                  if select._simple_int_clause(limit_clause):
                      limit_clause = limit_clause.render_literal_execute()
  
                  if select._simple_int_clause(offset_clause):
                      offset_clause = offset_clause.render_literal_execute()
  
                  # currently using form at:
                  # https://blogs.oracle.com/oraclemagazine/\
                  # on-rownum-and-limiting-results
  
                  orig_select = select
                  select = select._generate()
                  select._oracle_visit = True
  
                  # add expressions to accommodate FOR UPDATE OF
                  for_update = select._for_update_arg
                  if for_update is not None and for_update.of:
                      for_update = for_update._clone()
                      for_update._copy_internals()
  
                      for elem in for_update.of:
                          if not select.selected_columns.contains_column(elem):
                              select = select.add_columns(elem)
  
                  # Wrap the middle select and add the hint
                  inner_subquery = select.alias()
                  limitselect = sql.select(
                      *[
                          c
                          for c in inner_subquery.c
                          if orig_select.selected_columns.corresponding_column(c)
                          is not None
                      ]
                  )
  
                  if (
                      limit_clause is not None
                      and self.dialect.optimize_limits
                      and select._simple_int_clause(limit_clause)
                  ):
                      limitselect = limitselect.prefix_with(
                          expression.text(
                              "/*+ FIRST_ROWS(%s) */"
                              % self.process(limit_clause, **kwargs)
                          )
                      )
  
                  limitselect._oracle_visit = True
                  limitselect._is_wrapper = True
  
                  # add expressions to accommodate FOR UPDATE OF
                  if for_update is not None and for_update.of:
  
                      adapter = sql_util.ClauseAdapter(inner_subquery)
                      for_update.of = [
                          adapter.traverse(elem) for elem in for_update.of
                      ]
  
                  # If needed, add the limiting clause
                  if limit_clause is not None:
                      if select._simple_int_clause(limit_clause) and (
                          offset_clause is None
                          or select._simple_int_clause(offset_clause)
                      ):
                          max_row = limit_clause
  
                          if offset_clause is not None:
                              max_row = max_row + offset_clause
  
                      else:
                          max_row = limit_clause
  
                          if offset_clause is not None:
                              max_row = max_row + offset_clause
                      limitselect = limitselect.where(
                          sql.literal_column("ROWNUM") <= max_row
                      )
  
                  # If needed, add the ora_rn, and wrap again with offset.
                  if offset_clause is None:
                      limitselect._for_update_arg = for_update
                      select = limitselect
                  else:
                      limitselect = limitselect.add_columns(
                          sql.literal_column("ROWNUM").label("ora_rn")
                      )
                      limitselect._oracle_visit = True
                      limitselect._is_wrapper = True
  
                      if for_update is not None and for_update.of:
                          limitselect_cols = limitselect.selected_columns
                          for elem in for_update.of:
                              if (
                                  limitselect_cols.corresponding_column(elem)
                                  is None
                              ):
                                  limitselect = limitselect.add_columns(elem)
  
                      limit_subquery = limitselect.alias()
                      origselect_cols = orig_select.selected_columns
                      offsetselect = sql.select(
                          *[
                              c
                              for c in limit_subquery.c
                              if origselect_cols.corresponding_column(c)
                              is not None
                          ]
                      )
  
                      offsetselect._oracle_visit = True
                      offsetselect._is_wrapper = True
  
                      if for_update is not None and for_update.of:
                          adapter = sql_util.ClauseAdapter(limit_subquery)
                          for_update.of = [
                              adapter.traverse(elem) for elem in for_update.of
                          ]
  
                      offsetselect = offsetselect.where(
                          sql.literal_column("ora_rn") > offset_clause
                      )
  
                      offsetselect._for_update_arg = for_update
                      select = offsetselect
  
          return select
  
      def limit_clause(self, select, **kw):
          return ""
  
      def visit_empty_set_expr(self, type_):
          return "SELECT 1 FROM DUAL WHERE 1!=1"
  
      def for_update_clause(self, select, **kw):
          if self.is_subquery():
              return ""
  
          tmp = " FOR UPDATE"
  
          if select._for_update_arg.of:
              tmp += " OF " + ", ".join(
                  self.process(elem, **kw) for elem in select._for_update_arg.of
              )
  
          if select._for_update_arg.nowait:
              tmp += " NOWAIT"
          if select._for_update_arg.skip_locked:
              tmp += " SKIP LOCKED"
  
          return tmp
  
      def visit_is_distinct_from_binary(self, binary, operator, **kw):
          return "DECODE(%s, %s, 0, 1) = 1" % (
              self.process(binary.left),
              self.process(binary.right),
          )
  
      def visit_is_not_distinct_from_binary(self, binary, operator, **kw):
          return "DECODE(%s, %s, 0, 1) = 0" % (
              self.process(binary.left),
              self.process(binary.right),
          )
  
      def _get_regexp_args(self, binary, kw):
          string = self.process(binary.left, **kw)
          pattern = self.process(binary.right, **kw)
          flags = binary.modifiers["flags"]
          if flags is not None:
              flags = self.process(flags, **kw)
          return string, pattern, flags
  
      def visit_regexp_match_op_binary(self, binary, operator, **kw):
          string, pattern, flags = self._get_regexp_args(binary, kw)
          if flags is None:
              return "REGEXP_LIKE(%s, %s)" % (string, pattern)
          else:
              return "REGEXP_LIKE(%s, %s, %s)" % (string, pattern, flags)
  
      def visit_not_regexp_match_op_binary(self, binary, operator, **kw):
          return "NOT %s" % self.visit_regexp_match_op_binary(
              binary, operator, **kw
          )
  
      def visit_regexp_replace_op_binary(self, binary, operator, **kw):
          string, pattern, flags = self._get_regexp_args(binary, kw)
          replacement = self.process(binary.modifiers["replacement"], **kw)
          if flags is None:
              return "REGEXP_REPLACE(%s, %s, %s)" % (
                  string,
                  pattern,
                  replacement,
              )
          else:
              return "REGEXP_REPLACE(%s, %s, %s, %s)" % (
                  string,
                  pattern,
                  replacement,
                  flags,
              )
  
  
  class OracleDDLCompiler(compiler.DDLCompiler):
      def define_constraint_cascades(self, constraint):
          text = ""
          if constraint.ondelete is not None:
              text += " ON DELETE %s" % constraint.ondelete
  
          # oracle has no ON UPDATE CASCADE -
          # its only available via triggers
          # https://asktom.oracle.com/tkyte/update_cascade/index.html
          if constraint.onupdate is not None:
              util.warn(
                  "Oracle does not contain native UPDATE CASCADE "
                  "functionality - onupdates will not be rendered for foreign "
                  "keys.  Consider using deferrable=True, initially='deferred' "
                  "or triggers."
              )
  
          return text
  
      def visit_drop_table_comment(self, drop):
          return "COMMENT ON TABLE %s IS ''" % self.preparer.format_table(
              drop.element
          )
  
      def visit_create_index(self, create):
          index = create.element
          self._verify_index_table(index)
          preparer = self.preparer
          text = "CREATE "
          if index.unique:
              text += "UNIQUE "
          if index.dialect_options["oracle"]["bitmap"]:
              text += "BITMAP "
          text += "INDEX %s ON %s (%s)" % (
              self._prepared_index_name(index, include_schema=True),
              preparer.format_table(index.table, use_schema=True),
              ", ".join(
                  self.sql_compiler.process(
                      expr, include_table=False, literal_binds=True
                  )
                  for expr in index.expressions
              ),
          )
          if index.dialect_options["oracle"]["compress"] is not False:
              if index.dialect_options["oracle"]["compress"] is True:
                  text += " COMPRESS"
              else:
                  text += " COMPRESS %d" % (
                      index.dialect_options["oracle"]["compress"]
                  )
          return text
  
      def post_create_table(self, table):
          table_opts = []
          opts = table.dialect_options["oracle"]
  
          if opts["on_commit"]:
              on_commit_options = opts["on_commit"].replace("_", " ").upper()
              table_opts.append("\n ON COMMIT %s" % on_commit_options)
  
          if opts["compress"]:
              if opts["compress"] is True:
                  table_opts.append("\n COMPRESS")
              else:
                  table_opts.append("\n COMPRESS FOR %s" % (opts["compress"]))
  
          return "".join(table_opts)
  
      def get_identity_options(self, identity_options):
          text = super(OracleDDLCompiler, self).get_identity_options(
              identity_options
          )
          text = text.replace("NO MINVALUE", "NOMINVALUE")
          text = text.replace("NO MAXVALUE", "NOMAXVALUE")
          text = text.replace("NO CYCLE", "NOCYCLE")
          text = text.replace("NO ORDER", "NOORDER")
          return text
  
      def visit_computed_column(self, generated):
          text = "GENERATED ALWAYS AS (%s)" % self.sql_compiler.process(
              generated.sqltext, include_table=False, literal_binds=True
          )
          if generated.persisted is True:
              raise exc.CompileError(
                  "Oracle computed columns do not support 'stored' persistence; "
                  "set the 'persisted' flag to None or False for Oracle support."
              )
          elif generated.persisted is False:
              text += " VIRTUAL"
          return text
  
      def visit_identity_column(self, identity, **kw):
          if identity.always is None:
              kind = ""
          else:
              kind = "ALWAYS" if identity.always else "BY DEFAULT"
          text = "GENERATED %s" % kind
          if identity.on_null:
              text += " ON NULL"
          text += " AS IDENTITY"
          options = self.get_identity_options(identity)
          if options:
              text += " (%s)" % options
          return text
  
  
  class OracleIdentifierPreparer(compiler.IdentifierPreparer):
  
      reserved_words = {x.lower() for x in RESERVED_WORDS}
      illegal_initial_characters = {str(dig) for dig in range(0, 10)}.union(
          ["_", "$"]
      )
  
      def _bindparam_requires_quotes(self, value):
          """Return True if the given identifier requires quoting."""
          lc_value = value.lower()
          return (
              lc_value in self.reserved_words
              or value[0] in self.illegal_initial_characters
              or not self.legal_characters.match(str(value))
          )
  
      def format_savepoint(self, savepoint):
          name = savepoint.ident.lstrip("_")
          return super(OracleIdentifierPreparer, self).format_savepoint(
              savepoint, name
          )
  
  
  class OracleExecutionContext(default.DefaultExecutionContext):
      def fire_sequence(self, seq, type_):
          return self._execute_scalar(
              "SELECT "
              + self.identifier_preparer.format_sequence(seq)
              + ".nextval FROM DUAL",
              type_,
          )
  
  
  class OracleDialect(default.DefaultDialect):
      name = "oracle"
      supports_statement_cache = True
      supports_alter = True
      max_identifier_length = 128
  
      implicit_returning = True
  
      div_is_floordiv = False
  
      supports_simple_order_by_label = False
      cte_follows_insert = True
  
      supports_sequences = True
      sequences_optional = False
      postfetch_lastrowid = False
  
      default_paramstyle = "named"
      colspecs = colspecs
      ischema_names = ischema_names
      requires_name_normalize = True
  
      supports_comments = True
  
      supports_default_values = False
      supports_default_metavalue = True
      supports_empty_insert = False
      supports_identity_columns = True
  
      statement_compiler = OracleCompiler
      ddl_compiler = OracleDDLCompiler
      type_compiler = OracleTypeCompiler
      preparer = OracleIdentifierPreparer
      execution_ctx_cls = OracleExecutionContext
  
      reflection_options = ("oracle_resolve_synonyms",)
  
      _use_nchar_for_unicode = False
  
      construct_arguments = [
          (
              sa_schema.Table,
              {"resolve_synonyms": False, "on_commit": None, "compress": False},
          ),
          (sa_schema.Index, {"bitmap": False, "compress": False}),
      ]
  
      @util.deprecated_params(
          use_binds_for_limits=(
              "1.4",
              "The ``use_binds_for_limits`` Oracle dialect parameter is "
              "deprecated. The dialect now renders LIMIT /OFFSET integers "
              "inline in all cases using a post-compilation hook, so that the "
              "value is still represented by a 'bound parameter' on the Core "
              "Expression side.",
          )
      )
      def __init__(
          self,
          use_ansi=True,
          optimize_limits=False,
          use_binds_for_limits=None,
          use_nchar_for_unicode=False,
          exclude_tablespaces=("SYSTEM", "SYSAUX"),
          **kwargs,
      ):
          default.DefaultDialect.__init__(self, **kwargs)
          self._use_nchar_for_unicode = use_nchar_for_unicode
          self.use_ansi = use_ansi
          self.optimize_limits = optimize_limits
          self.exclude_tablespaces = exclude_tablespaces
  
      def initialize(self, connection):
          super(OracleDialect, self).initialize(connection)
  
          # Oracle 8i has RETURNING:
          # https://docs.oracle.com/cd/A87860_01/doc/index.htm
  
          # so does Oracle8:
          # https://docs.oracle.com/cd/A64702_01/doc/index.htm
  
          if self._is_oracle_8:
              self.colspecs = self.colspecs.copy()
              self.colspecs.pop(sqltypes.Interval)
              self.use_ansi = False
  
          self.supports_identity_columns = self.server_version_info >= (12,)
  
      def _get_effective_compat_server_version_info(self, connection):
          # dialect does not need compat levels below 12.2, so don't query
          # in those cases
  
          if self.server_version_info < (12, 2):
              return self.server_version_info
          try:
              compat = connection.exec_driver_sql(
                  "SELECT value FROM v$parameter WHERE name = 'compatible'"
              ).scalar()
          except exc.DBAPIError:
              compat = None
  
          if compat:
              try:
                  return tuple(int(x) for x in compat.split("."))
              except:
                  return self.server_version_info
          else:
              return self.server_version_info
  
      @property
      def _is_oracle_8(self):
          return self.server_version_info and self.server_version_info < (9,)
  
      @property
      def _supports_table_compression(self):
          return self.server_version_info and self.server_version_info >= (10, 1)
  
      @property
      def _supports_table_compress_for(self):
          return self.server_version_info and self.server_version_info >= (11,)
  
      @property
      def _supports_char_length(self):
          return not self._is_oracle_8
  
      @property
      def _supports_update_returning_computed_cols(self):
          # on version 18 this error is no longet present while it happens on 11
          # it may work also on versions before the 18
          return self.server_version_info and self.server_version_info >= (18,)
  
      def do_release_savepoint(self, connection, name):
          # Oracle does not support RELEASE SAVEPOINT
          pass
  
      def _check_max_identifier_length(self, connection):
          if self._get_effective_compat_server_version_info(connection) < (
              12,
              2,
          ):
              return 30
          else:
              # use the default
              return None
  
      def get_isolation_level_values(self, dbapi_connection):
          return ["READ COMMITTED", "SERIALIZABLE"]
  
      def get_default_isolation_level(self, dbapi_conn):
          try:
              return self.get_isolation_level(dbapi_conn)
          except NotImplementedError:
              raise
          except:
              return "READ COMMITTED"
  
      def has_table(self, connection, table_name, schema=None):
          self._ensure_has_table_connection(connection)
  
          if not schema:
              schema = self.default_schema_name
  
          cursor = connection.execute(
              sql.text(
                  """SELECT table_name FROM all_tables
                  WHERE table_name = CAST(:name AS VARCHAR2(128))
                  AND owner = CAST(:schema_name AS VARCHAR2(128))
                  UNION ALL
                  SELECT view_name FROM all_views
                  WHERE view_name = CAST(:name AS VARCHAR2(128))
                  AND owner = CAST(:schema_name AS VARCHAR2(128))
                  """
              ),
              dict(
                  name=self.denormalize_name(table_name),
                  schema_name=self.denormalize_name(schema),
              ),
          )
          return cursor.first() is not None
  
      def has_sequence(self, connection, sequence_name, schema=None):
          if not schema:
              schema = self.default_schema_name
          cursor = connection.execute(
              sql.text(
                  "SELECT sequence_name FROM all_sequences "
                  "WHERE sequence_name = :name AND "
                  "sequence_owner = :schema_name"
              ),
              dict(
                  name=self.denormalize_name(sequence_name),
                  schema_name=self.denormalize_name(schema),
              ),
          )
          return cursor.first() is not None
  
      def _get_default_schema_name(self, connection):
          return self.normalize_name(
              connection.exec_driver_sql(
                  "select sys_context( 'userenv', 'current_schema' ) from dual"
              ).scalar()
          )
  
      def _resolve_synonym(
          self,
          connection,
          desired_owner=None,
          desired_synonym=None,
          desired_table=None,
      ):
          """search for a local synonym matching the given desired owner/name.
  
          if desired_owner is None, attempts to locate a distinct owner.
  
          returns the actual name, owner, dblink name, and synonym name if
          found.
          """
  
          q = (
              "SELECT owner, table_owner, table_name, db_link, "
              "synonym_name FROM all_synonyms WHERE "
          )
          clauses = []
          params = {}
          if desired_synonym:
              clauses.append(
                  "synonym_name = CAST(:synonym_name AS VARCHAR2(128))"
              )
              params["synonym_name"] = desired_synonym
          if desired_owner:
              clauses.append("owner = CAST(:desired_owner AS VARCHAR2(128))")
              params["desired_owner"] = desired_owner
          if desired_table:
              clauses.append("table_name = CAST(:tname AS VARCHAR2(128))")
              params["tname"] = desired_table
  
          q += " AND ".join(clauses)
  
          result = connection.execution_options(future_result=True).execute(
              sql.text(q), params
          )
          if desired_owner:
              row = result.mappings().first()
              if row:
                  return (
                      row["table_name"],
                      row["table_owner"],
                      row["db_link"],
                      row["synonym_name"],
                  )
              else:
                  return None, None, None, None
          else:
              rows = result.mappings().all()
              if len(rows) > 1:
                  raise AssertionError(
                      "There are multiple tables visible to the schema, you "
                      "must specify owner"
                  )
              elif len(rows) == 1:
                  row = rows[0]
                  return (
                      row["table_name"],
                      row["table_owner"],
                      row["db_link"],
                      row["synonym_name"],
                  )
              else:
                  return None, None, None, None
  
      @reflection.cache
      def _prepare_reflection_args(
          self,
          connection,
          table_name,
          schema=None,
          resolve_synonyms=False,
          dblink="",
          **kw,
      ):
  
          if resolve_synonyms:
              actual_name, owner, dblink, synonym = self._resolve_synonym(
                  connection,
                  desired_owner=self.denormalize_name(schema),
                  desired_synonym=self.denormalize_name(table_name),
              )
          else:
              actual_name, owner, dblink, synonym = None, None, None, None
          if not actual_name:
              actual_name = self.denormalize_name(table_name)
  
          if dblink:
              # using user_db_links here since all_db_links appears
              # to have more restricted permissions.
              # https://docs.oracle.com/cd/B28359_01/server.111/b28310/ds_admin005.htm
              # will need to hear from more users if we are doing
              # the right thing here.  See [ticket:2619]
              owner = connection.scalar(
                  sql.text(
                      "SELECT username FROM user_db_links " "WHERE db_link=:link"
                  ),
                  dict(link=dblink),
              )
              dblink = "@" + dblink
          elif not owner:
              owner = self.denormalize_name(schema or self.default_schema_name)
  
          return (actual_name, owner, dblink or "", synonym)
  
      @reflection.cache
      def get_schema_names(self, connection, **kw):
          s = "SELECT username FROM all_users ORDER BY username"
          cursor = connection.exec_driver_sql(s)
          return [self.normalize_name(row[0]) for row in cursor]
  
      @reflection.cache
      def get_table_names(self, connection, schema=None, **kw):
          schema = self.denormalize_name(schema or self.default_schema_name)
  
          # note that table_names() isn't loading DBLINKed or synonym'ed tables
          if schema is None:
              schema = self.default_schema_name
  
          sql_str = "SELECT table_name FROM all_tables WHERE "
          if self.exclude_tablespaces:
              sql_str += (
                  "nvl(tablespace_name, 'no tablespace') "
                  "NOT IN (%s) AND "
                  % (", ".join(["'%s'" % ts for ts in self.exclude_tablespaces]))
              )
          sql_str += (
              "OWNER = :owner " "AND IOT_NAME IS NULL " "AND DURATION IS NULL"
          )
  
          cursor = connection.execute(sql.text(sql_str), dict(owner=schema))
          return [self.normalize_name(row[0]) for row in cursor]
  
      @reflection.cache
      def get_temp_table_names(self, connection, **kw):
          schema = self.denormalize_name(self.default_schema_name)
  
          sql_str = "SELECT table_name FROM all_tables WHERE "
          if self.exclude_tablespaces:
              sql_str += (
                  "nvl(tablespace_name, 'no tablespace') "
                  "NOT IN (%s) AND "
                  % (", ".join(["'%s'" % ts for ts in self.exclude_tablespaces]))
              )
          sql_str += (
              "OWNER = :owner "
              "AND IOT_NAME IS NULL "
              "AND DURATION IS NOT NULL"
          )
  
          cursor = connection.execute(sql.text(sql_str), dict(owner=schema))
          return [self.normalize_name(row[0]) for row in cursor]
  
      @reflection.cache
      def get_view_names(self, connection, schema=None, **kw):
          schema = self.denormalize_name(schema or self.default_schema_name)
          s = sql.text("SELECT view_name FROM all_views WHERE owner = :owner")
          cursor = connection.execute(
              s, dict(owner=self.denormalize_name(schema))
          )
          return [self.normalize_name(row[0]) for row in cursor]
  
      @reflection.cache
      def get_sequence_names(self, connection, schema=None, **kw):
          if not schema:
              schema = self.default_schema_name
          cursor = connection.execute(
              sql.text(
                  "SELECT sequence_name FROM all_sequences "
                  "WHERE sequence_owner = :schema_name"
              ),
              dict(schema_name=self.denormalize_name(schema)),
          )
          return [self.normalize_name(row[0]) for row in cursor]
  
      @reflection.cache
      def get_table_options(self, connection, table_name, schema=None, **kw):
          options = {}
  
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          params = {"table_name": table_name}
  
          columns = ["table_name"]
          if self._supports_table_compression:
              columns.append("compression")
          if self._supports_table_compress_for:
              columns.append("compress_for")
  
          text = (
              "SELECT %(columns)s "
              "FROM ALL_TABLES%(dblink)s "
              "WHERE table_name = CAST(:table_name AS VARCHAR(128))"
          )
  
          if schema is not None:
              params["owner"] = schema
              text += " AND owner = CAST(:owner AS VARCHAR(128)) "
          text = text % {"dblink": dblink, "columns": ", ".join(columns)}
  
          result = connection.execute(sql.text(text), params)
  
          enabled = dict(DISABLED=False, ENABLED=True)
  
          row = result.first()
          if row:
              if "compression" in row._fields and enabled.get(
                  row.compression, False
              ):
                  if "compress_for" in row._fields:
                      options["oracle_compress"] = row.compress_for
                  else:
                      options["oracle_compress"] = True
  
          return options
  
      @reflection.cache
      def get_columns(self, connection, table_name, schema=None, **kw):
          """
  
          kw arguments can be:
  
              oracle_resolve_synonyms
  
              dblink
  
          """
  
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
          columns = []
          if self._supports_char_length:
              char_length_col = "char_length"
          else:
              char_length_col = "data_length"
  
          if self.server_version_info >= (12,):
              identity_cols = """\
                  col.default_on_null,
                  (
                      SELECT id.generation_type || ',' || id.IDENTITY_OPTIONS
                      FROM ALL_TAB_IDENTITY_COLS%(dblink)s id
                      WHERE col.table_name = id.table_name
                      AND col.column_name = id.column_name
                      AND col.owner = id.owner
                  ) AS identity_options""" % {
                  "dblink": dblink
              }
          else:
              identity_cols = "NULL as default_on_null, NULL as identity_options"
  
          params = {"table_name": table_name}
  
          text = """
              SELECT
                  col.column_name,
                  col.data_type,
                  col.%(char_length_col)s,
                  col.data_precision,
                  col.data_scale,
                  col.nullable,
                  col.data_default,
                  com.comments,
                  col.virtual_column,
                  %(identity_cols)s
              FROM all_tab_cols%(dblink)s col
              LEFT JOIN all_col_comments%(dblink)s com
              ON col.table_name = com.table_name
              AND col.column_name = com.column_name
              AND col.owner = com.owner
              WHERE col.table_name = CAST(:table_name AS VARCHAR2(128))
              AND col.hidden_column = 'NO'
          """
          if schema is not None:
              params["owner"] = schema
              text += " AND col.owner = :owner "
          text += " ORDER BY col.column_id"
          text = text % {
              "dblink": dblink,
              "char_length_col": char_length_col,
              "identity_cols": identity_cols,
          }
  
          c = connection.execute(sql.text(text), params)
  
          for row in c:
              colname = self.normalize_name(row[0])
              orig_colname = row[0]
              coltype = row[1]
              length = row[2]
              precision = row[3]
              scale = row[4]
              nullable = row[5] == "Y"
              default = row[6]
              comment = row[7]
              generated = row[8]
              default_on_nul = row[9]
              identity_options = row[10]
  
              if coltype == "NUMBER":
                  if precision is None and scale == 0:
                      coltype = INTEGER()
                  else:
                      coltype = NUMBER(precision, scale)
              elif coltype == "FLOAT":
                  # TODO: support "precision" here as "binary_precision"
                  coltype = FLOAT()
              elif coltype in ("VARCHAR2", "NVARCHAR2", "CHAR", "NCHAR"):
                  coltype = self.ischema_names.get(coltype)(length)
              elif "WITH TIME ZONE" in coltype:
                  coltype = TIMESTAMP(timezone=True)
              else:
                  coltype = re.sub(r"\(\d+\)", "", coltype)
                  try:
                      coltype = self.ischema_names[coltype]
                  except KeyError:
                      util.warn(
                          "Did not recognize type '%s' of column '%s'"
                          % (coltype, colname)
                      )
                      coltype = sqltypes.NULLTYPE
  
              if generated == "YES":
                  computed = dict(sqltext=default)
                  default = None
              else:
                  computed = None
  
              if identity_options is not None:
                  identity = self._parse_identity_options(
                      identity_options, default_on_nul
                  )
                  default = None
              else:
                  identity = None
  
              cdict = {
                  "name": colname,
                  "type": coltype,
                  "nullable": nullable,
                  "default": default,
                  "autoincrement": "auto",
                  "comment": comment,
              }
              if orig_colname.lower() == orig_colname:
                  cdict["quote"] = True
              if computed is not None:
                  cdict["computed"] = computed
              if identity is not None:
                  cdict["identity"] = identity
  
              columns.append(cdict)
          return columns
  
      def _parse_identity_options(self, identity_options, default_on_nul):
          # identity_options is a string that starts with 'ALWAYS,' or
          # 'BY DEFAULT,' and continues with
          # START WITH: 1, INCREMENT BY: 1, MAX_VALUE: 123, MIN_VALUE: 1,
          # CYCLE_FLAG: N, CACHE_SIZE: 1, ORDER_FLAG: N, SCALE_FLAG: N,
          # EXTEND_FLAG: N, SESSION_FLAG: N, KEEP_VALUE: N
          parts = [p.strip() for p in identity_options.split(",")]
          identity = {
              "always": parts[0] == "ALWAYS",
              "on_null": default_on_nul == "YES",
          }
  
          for part in parts[1:]:
              option, value = part.split(":")
              value = value.strip()
  
              if "START WITH" in option:
                  identity["start"] = int(value)
              elif "INCREMENT BY" in option:
                  identity["increment"] = int(value)
              elif "MAX_VALUE" in option:
                  identity["maxvalue"] = int(value)
              elif "MIN_VALUE" in option:
                  identity["minvalue"] = int(value)
              elif "CYCLE_FLAG" in option:
                  identity["cycle"] = value == "Y"
              elif "CACHE_SIZE" in option:
                  identity["cache"] = int(value)
              elif "ORDER_FLAG" in option:
                  identity["order"] = value == "Y"
          return identity
  
      @reflection.cache
      def get_table_comment(
          self,
          connection,
          table_name,
          schema=None,
          resolve_synonyms=False,
          dblink="",
          **kw,
      ):
  
          info_cache = kw.get("info_cache")
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          if not schema:
              schema = self.default_schema_name
  
          COMMENT_SQL = """
              SELECT comments
              FROM all_tab_comments
              WHERE table_name = CAST(:table_name AS VARCHAR(128))
              AND owner = CAST(:schema_name AS VARCHAR(128))
          """
  
          c = connection.execute(
              sql.text(COMMENT_SQL),
              dict(table_name=table_name, schema_name=schema),
          )
          return {"text": c.scalar()}
  
      @reflection.cache
      def get_indexes(
          self,
          connection,
          table_name,
          schema=None,
          resolve_synonyms=False,
          dblink="",
          **kw,
      ):
  
          info_cache = kw.get("info_cache")
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
          indexes = []
  
          params = {"table_name": table_name}
          text = (
              "SELECT a.index_name, a.column_name, "
              "\nb.index_type, b.uniqueness, b.compression, b.prefix_length "
              "\nFROM ALL_IND_COLUMNS%(dblink)s a, "
              "\nALL_INDEXES%(dblink)s b "
              "\nWHERE "
              "\na.index_name = b.index_name "
              "\nAND a.table_owner = b.table_owner "
              "\nAND a.table_name = b.table_name "
              "\nAND a.table_name = CAST(:table_name AS VARCHAR(128))"
          )
  
          if schema is not None:
              params["schema"] = schema
              text += "AND a.table_owner = :schema "
  
          text += "ORDER BY a.index_name, a.column_position"
  
          text = text % {"dblink": dblink}
  
          q = sql.text(text)
          rp = connection.execute(q, params)
          indexes = []
          last_index_name = None
          pk_constraint = self.get_pk_constraint(
              connection,
              table_name,
              schema,
              resolve_synonyms=resolve_synonyms,
              dblink=dblink,
              info_cache=kw.get("info_cache"),
          )
  
          uniqueness = dict(NONUNIQUE=False, UNIQUE=True)
          enabled = dict(DISABLED=False, ENABLED=True)
  
          oracle_sys_col = re.compile(r"SYS_NC\d+\$", re.IGNORECASE)
  
          index = None
          for rset in rp:
              index_name_normalized = self.normalize_name(rset.index_name)
  
              # skip primary key index.  This is refined as of
              # [ticket:5421].  Note that ALL_INDEXES.GENERATED will by "Y"
              # if the name of this index was generated by Oracle, however
              # if a named primary key constraint was created then this flag
              # is false.
              if (
                  pk_constraint
                  and index_name_normalized == pk_constraint["name"]
              ):
                  continue
  
              if rset.index_name != last_index_name:
                  index = dict(
                      name=index_name_normalized,
                      column_names=[],
                      dialect_options={},
                  )
                  indexes.append(index)
              index["unique"] = uniqueness.get(rset.uniqueness, False)
  
              if rset.index_type in ("BITMAP", "FUNCTION-BASED BITMAP"):
                  index["dialect_options"]["oracle_bitmap"] = True
              if enabled.get(rset.compression, False):
                  index["dialect_options"][
                      "oracle_compress"
                  ] = rset.prefix_length
  
              # filter out Oracle SYS_NC names.  could also do an outer join
              # to the all_tab_columns table and check for real col names there.
              if not oracle_sys_col.match(rset.column_name):
                  index["column_names"].append(
                      self.normalize_name(rset.column_name)
                  )
              last_index_name = rset.index_name
  
          return indexes
  
      @reflection.cache
      def _get_constraint_data(
          self, connection, table_name, schema=None, dblink="", **kw
      ):
  
          params = {"table_name": table_name}
  
          text = (
              "SELECT"
              "\nac.constraint_name,"  # 0
              "\nac.constraint_type,"  # 1
              "\nloc.column_name AS local_column,"  # 2
              "\nrem.table_name AS remote_table,"  # 3
              "\nrem.column_name AS remote_column,"  # 4
              "\nrem.owner AS remote_owner,"  # 5
              "\nloc.position as loc_pos,"  # 6
              "\nrem.position as rem_pos,"  # 7
              "\nac.search_condition,"  # 8
              "\nac.delete_rule"  # 9
              "\nFROM all_constraints%(dblink)s ac,"
              "\nall_cons_columns%(dblink)s loc,"
              "\nall_cons_columns%(dblink)s rem"
              "\nWHERE ac.table_name = CAST(:table_name AS VARCHAR2(128))"
              "\nAND ac.constraint_type IN ('R','P', 'U', 'C')"
          )
  
          if schema is not None:
              params["owner"] = schema
              text += "\nAND ac.owner = CAST(:owner AS VARCHAR2(128))"
  
          text += (
              "\nAND ac.owner = loc.owner"
              "\nAND ac.constraint_name = loc.constraint_name"
              "\nAND ac.r_owner = rem.owner(+)"
              "\nAND ac.r_constraint_name = rem.constraint_name(+)"
              "\nAND (rem.position IS NULL or loc.position=rem.position)"
              "\nORDER BY ac.constraint_name, loc.position"
          )
  
          text = text % {"dblink": dblink}
          rp = connection.execute(sql.text(text), params)
          constraint_data = rp.fetchall()
          return constraint_data
  
      @reflection.cache
      def get_pk_constraint(self, connection, table_name, schema=None, **kw):
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
          pkeys = []
          constraint_name = None
          constraint_data = self._get_constraint_data(
              connection,
              table_name,
              schema,
              dblink,
              info_cache=kw.get("info_cache"),
          )
  
          for row in constraint_data:
              (
                  cons_name,
                  cons_type,
                  local_column,
                  remote_table,
                  remote_column,
                  remote_owner,
              ) = row[0:2] + tuple([self.normalize_name(x) for x in row[2:6]])
              if cons_type == "P":
                  if constraint_name is None:
                      constraint_name = self.normalize_name(cons_name)
                  pkeys.append(local_column)
          return {"constrained_columns": pkeys, "name": constraint_name}
  
      @reflection.cache
      def get_foreign_keys(self, connection, table_name, schema=None, **kw):
          """
  
          kw arguments can be:
  
              oracle_resolve_synonyms
  
              dblink
  
          """
          requested_schema = schema  # to check later on
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          constraint_data = self._get_constraint_data(
              connection,
              table_name,
              schema,
              dblink,
              info_cache=kw.get("info_cache"),
          )
  
          def fkey_rec():
              return {
                  "name": None,
                  "constrained_columns": [],
                  "referred_schema": None,
                  "referred_table": None,
                  "referred_columns": [],
                  "options": {},
              }
  
          fkeys = util.defaultdict(fkey_rec)
  
          for row in constraint_data:
              (
                  cons_name,
                  cons_type,
                  local_column,
                  remote_table,
                  remote_column,
                  remote_owner,
              ) = row[0:2] + tuple([self.normalize_name(x) for x in row[2:6]])
  
              cons_name = self.normalize_name(cons_name)
  
              if cons_type == "R":
                  if remote_table is None:
                      # ticket 363
                      util.warn(
                          (
                              "Got 'None' querying 'table_name' from "
                              "all_cons_columns%(dblink)s - does the user have "
                              "proper rights to the table?"
                          )
                          % {"dblink": dblink}
                      )
                      continue
  
                  rec = fkeys[cons_name]
                  rec["name"] = cons_name
                  local_cols, remote_cols = (
                      rec["constrained_columns"],
                      rec["referred_columns"],
                  )
  
                  if not rec["referred_table"]:
                      if resolve_synonyms:
                          (
                              ref_remote_name,
                              ref_remote_owner,
                              ref_dblink,
                              ref_synonym,
                          ) = self._resolve_synonym(
                              connection,
                              desired_owner=self.denormalize_name(remote_owner),
                              desired_table=self.denormalize_name(remote_table),
                          )
                          if ref_synonym:
                              remote_table = self.normalize_name(ref_synonym)
                              remote_owner = self.normalize_name(
                                  ref_remote_owner
                              )
  
                      rec["referred_table"] = remote_table
  
                      if (
                          requested_schema is not None
                          or self.denormalize_name(remote_owner) != schema
                      ):
                          rec["referred_schema"] = remote_owner
  
                      if row[9] != "NO ACTION":
                          rec["options"]["ondelete"] = row[9]
  
                  local_cols.append(local_column)
                  remote_cols.append(remote_column)
  
          return list(fkeys.values())
  
      @reflection.cache
      def get_unique_constraints(
          self, connection, table_name, schema=None, **kw
      ):
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          constraint_data = self._get_constraint_data(
              connection,
              table_name,
              schema,
              dblink,
              info_cache=kw.get("info_cache"),
          )
  
          unique_keys = filter(lambda x: x[1] == "U", constraint_data)
          uniques_group = groupby(unique_keys, lambda x: x[0])
  
          index_names = {
              ix["name"]
              for ix in self.get_indexes(connection, table_name, schema=schema)
          }
          return [
              {
                  "name": name,
                  "column_names": cols,
                  "duplicates_index": name if name in index_names else None,
              }
              for name, cols in [
                  [
                      self.normalize_name(i[0]),
                      [self.normalize_name(x[2]) for x in i[1]],
                  ]
                  for i in uniques_group
              ]
          ]
  
      @reflection.cache
      def get_view_definition(
          self,
          connection,
          view_name,
          schema=None,
          resolve_synonyms=False,
          dblink="",
          **kw,
      ):
          info_cache = kw.get("info_cache")
          (view_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              view_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          params = {"view_name": view_name}
          text = "SELECT text FROM all_views WHERE view_name=:view_name"
  
          if schema is not None:
              text += " AND owner = :schema"
              params["schema"] = schema
  
          rp = connection.execute(sql.text(text), params).scalar()
          if rp:
              return rp
          else:
              return None
  
      @reflection.cache
      def get_check_constraints(
          self, connection, table_name, schema=None, include_all=False, **kw
      ):
          resolve_synonyms = kw.get("oracle_resolve_synonyms", False)
          dblink = kw.get("dblink", "")
          info_cache = kw.get("info_cache")
  
          (table_name, schema, dblink, synonym) = self._prepare_reflection_args(
              connection,
              table_name,
              schema,
              resolve_synonyms,
              dblink,
              info_cache=info_cache,
          )
  
          constraint_data = self._get_constraint_data(
              connection,
              table_name,
              schema,
              dblink,
              info_cache=kw.get("info_cache"),
          )
  
          check_constraints = filter(lambda x: x[1] == "C", constraint_data)
  
          return [
              {"name": self.normalize_name(cons[0]), "sqltext": cons[8]}
              for cons in check_constraints
              if include_all or not re.match(r"..+?. IS NOT NULL$", cons[8])
          ]
  
  
  class _OuterJoinColumn(sql.ClauseElement):
      __visit_name__ = "outer_join_column"
  
      def __init__(self, column):
          self.column = column
  