# mysql/base.py
# Copyright (C) 2005-2014 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

"""

.. dialect:: mysql
    :name: MySQL

Supported Versions and Features
-------------------------------

SQLAlchemy supports MySQL starting with version 4.1 through modern releases.
However, no heroic measures are taken to work around major missing
SQL features - if your server version does not support sub-selects, for
example, they won't work in SQLAlchemy either.

See the official MySQL documentation for detailed information about features
supported in any given server release.

.. _mysql_connection_timeouts:

Connection Timeouts
-------------------

MySQL features an automatic connection close behavior, for connections that have
been idle for eight hours or more.   To circumvent having this issue, use the
``pool_recycle`` option which controls the maximum age of any connection::

    engine = create_engine('mysql+mysqldb://...', pool_recycle=3600)

.. _mysql_storage_engines:

CREATE TABLE arguments including Storage Engines
------------------------------------------------

MySQL's CREATE TABLE syntax includes a wide array of special options,
including ``ENGINE``, ``CHARSET``, ``MAX_ROWS``, ``ROW_FORMAT``, ``INSERT_METHOD``, and many more.
To accommodate the rendering of these arguments, specify the form
``mysql_argument_name="value"``.  For example, to specify a table with
``ENGINE`` of ``InnoDB``, ``CHARSET`` of ``utf8``, and ``KEY_BLOCK_SIZE`` of ``1024``::

  Table('mytable', metadata,
        Column('data', String(32)),
        mysql_engine='InnoDB',
        mysql_charset='utf8',
        mysql_key_block_size="1024"
       )

The MySQL dialect will normally transfer any keyword specified as ``mysql_keyword_name``
to be rendered as ``KEYWORD_NAME`` in the ``CREATE TABLE`` statement.  A handful
of these names will render with a space instead of an underscore; to support this,
the MySQL dialect has awareness of these particular names, which include
``DATA DIRECTORY`` (e.g. ``mysql_data_directory``), ``CHARACTER SET`` (e.g.
``mysql_character_set``) and ``INDEX DIRECTORY`` (e.g. ``mysql_index_directory``).

The most common argument is ``mysql_engine``, which refers to the storage engine
for the table.  Historically, MySQL server installations would default
to ``MyISAM`` for this value, although newer versions may be defaulting
to ``InnoDB``.  The ``InnoDB`` engine is typically preferred for its support
of transactions and foreign keys.

A :class:`.Table` that is created in a MySQL database with a storage engine
of ``MyISAM`` will be essentially non-transactional, meaning any INSERT/UPDATE/DELETE
statement referring to this table will be invoked as autocommit.   It also will have no
support for foreign key constraints; while the ``CREATE TABLE`` statement
accepts foreign key options, when using the ``MyISAM`` storage engine these
arguments are discarded.  Reflecting such a table will also produce no
foreign key constraint information.

For fully atomic transactions as well as support for foreign key
constraints, all participating ``CREATE TABLE`` statements must specify a
transactional engine, which in the vast majority of cases is ``InnoDB``.

.. seealso::

    `The InnoDB Storage Engine
    <http://dev.mysql.com/doc/refman/5.0/en/innodb-storage-engine.html>`_ -
    on the MySQL website.

Case Sensitivity and Table Reflection
-------------------------------------

MySQL has inconsistent support for case-sensitive identifier
names, basing support on specific details of the underlying
operating system. However, it has been observed that no matter
what case sensitivity behavior is present, the names of tables in
foreign key declarations are *always* received from the database
as all-lower case, making it impossible to accurately reflect a
schema where inter-related tables use mixed-case identifier names.

Therefore it is strongly advised that table names be declared as
all lower case both within SQLAlchemy as well as on the MySQL
database itself, especially if database reflection features are
to be used.

Transaction Isolation Level
---------------------------

:func:`.create_engine` accepts an ``isolation_level``
parameter which results in the command ``SET SESSION
TRANSACTION ISOLATION LEVEL <level>`` being invoked for
every new connection. Valid values for this parameter are
``READ COMMITTED``, ``READ UNCOMMITTED``,
``REPEATABLE READ``, and ``SERIALIZABLE``::

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

.. versionadded:: 0.7.6

AUTO_INCREMENT Behavior
-----------------------

When creating tables, SQLAlchemy will automatically set ``AUTO_INCREMENT`` on
the first :class:`.Integer` primary key column which is not marked as a foreign key::

  >>> t = Table('mytable', metadata,
  ...   Column('mytable_id', Integer, primary_key=True)
  ... )
  >>> t.create()
  CREATE TABLE mytable (
          id INTEGER NOT NULL AUTO_INCREMENT,
          PRIMARY KEY (id)
  )

You can disable this behavior by passing ``False`` to the :paramref:`~.Column.autoincrement`
argument of :class:`.Column`.  This flag can also be used to enable
auto-increment on a secondary column in a multi-column key for some storage
engines::

  Table('mytable', metadata,
        Column('gid', Integer, primary_key=True, autoincrement=False),
        Column('id', Integer, primary_key=True)
       )

Ansi Quoting Style
------------------

MySQL features two varieties of identifier "quoting style", one using
backticks and the other using quotes, e.g. ```some_identifier```  vs.
``"some_identifier"``.   All MySQL dialects detect which version
is in use by checking the value of ``sql_mode`` when a connection is first
established with a particular :class:`.Engine`.  This quoting style comes
into play when rendering table and column names as well as when reflecting
existing database structures.  The detection is entirely automatic and
no special configuration is needed to use either quoting style.

.. versionchanged:: 0.6 detection of ANSI quoting style is entirely automatic,
   there's no longer any end-user ``create_engine()`` options in this regard.

MySQL SQL Extensions
--------------------

Many of the MySQL SQL extensions are handled through SQLAlchemy's generic
function and operator support::

  table.select(table.c.password==func.md5('plaintext'))
  table.select(table.c.username.op('regexp')('^[a-d]'))

And of course any valid MySQL statement can be executed as a string as well.

Some limited direct support for MySQL extensions to SQL is currently
available.

* SELECT pragma::

    select(..., prefixes=['HIGH_PRIORITY', 'SQL_SMALL_RESULT'])

* UPDATE with LIMIT::

    update(..., mysql_limit=10)

rowcount Support
----------------

SQLAlchemy standardizes the DBAPI ``cursor.rowcount`` attribute to be the
usual definition of "number of rows matched by an UPDATE or DELETE" statement.
This is in contradiction to the default setting on most MySQL DBAPI drivers,
which is "number of rows actually modified/deleted".  For this reason, the
SQLAlchemy MySQL dialects always set the ``constants.CLIENT.FOUND_ROWS`` flag,
or whatever is equivalent for the DBAPI in use, on connect, unless the flag value
is overridden using DBAPI-specific options
(such as ``client_flag`` for the MySQL-Python driver, ``found_rows`` for the
OurSQL driver).

See also:

:attr:`.ResultProxy.rowcount`


CAST Support
------------

MySQL documents the CAST operator as available in version 4.0.2.  When using the
SQLAlchemy :func:`.cast` function, SQLAlchemy
will not render the CAST token on MySQL before this version, based on server version
detection, instead rendering the internal expression directly.

CAST may still not be desirable on an early MySQL version post-4.0.2, as it didn't
add all datatype support until 4.1.1.   If your application falls into this
narrow area, the behavior of CAST can be controlled using the
:ref:`sqlalchemy.ext.compiler_toplevel` system, as per the recipe below::

    from sqlalchemy.sql.expression import Cast
    from sqlalchemy.ext.compiler import compiles

    @compiles(Cast, 'mysql')
    def _check_mysql_version(element, compiler, **kw):
        if compiler.dialect.server_version_info < (4, 1, 0):
            return compiler.process(element.clause, **kw)
        else:
            return compiler.visit_cast(element, **kw)

The above function, which only needs to be declared once
within an application, overrides the compilation of the
:func:`.cast` construct to check for version 4.1.0 before
fully rendering CAST; else the internal element of the
construct is rendered directly.


.. _mysql_indexes:

MySQL Specific Index Options
----------------------------

MySQL-specific extensions to the :class:`.Index` construct are available.

Index Length
~~~~~~~~~~~~~

MySQL provides an option to create index entries with a certain length, where
"length" refers to the number of characters or bytes in each value which will
become part of the index. SQLAlchemy provides this feature via the
``mysql_length`` parameter::

    Index('my_index', my_table.c.data, mysql_length=10)

    Index('a_b_idx', my_table.c.a, my_table.c.b, mysql_length={'a': 4, 'b': 9})

Prefix lengths are given in characters for nonbinary string types and in bytes
for binary string types. The value passed to the keyword argument *must* be
either an integer (and, thus, specify the same prefix length value for all
columns of the index) or a dict in which keys are column names and values are
prefix length values for corresponding columns. MySQL only allows a length for
a column of an index if it is for a CHAR, VARCHAR, TEXT, BINARY, VARBINARY and
BLOB.

.. versionadded:: 0.8.2 ``mysql_length`` may now be specified as a dictionary
   for use with composite indexes.

Index Types
~~~~~~~~~~~~~

Some MySQL storage engines permit you to specify an index type when creating
an index or primary key constraint. SQLAlchemy provides this feature via the
``mysql_using`` parameter on :class:`.Index`::

    Index('my_index', my_table.c.data, mysql_using='hash')

As well as the ``mysql_using`` parameter on :class:`.PrimaryKeyConstraint`::

    PrimaryKeyConstraint("data", mysql_using='hash')

The value passed to the keyword argument will be simply passed through to the
underlying CREATE INDEX or PRIMARY KEY clause, so it *must* be a valid index
type for your MySQL storage engine.

More information can be found at:

http://dev.mysql.com/doc/refman/5.0/en/create-index.html

http://dev.mysql.com/doc/refman/5.0/en/create-table.html

.. _mysql_foreign_keys:

MySQL Foreign Keys
------------------

MySQL's behavior regarding foreign keys has some important caveats.

Foreign Key Arguments to Avoid
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

MySQL does not support the foreign key arguments "DEFERRABLE", "INITIALLY",
or "MATCH".  Using the ``deferrable`` or ``initially`` keyword argument with
:class:`.ForeignKeyConstraint` or :class:`.ForeignKey` will have the effect of
these keywords being ignored in a DDL expression along with a warning, however this behavior
**will change** in a future release.

In order to use these keywords on a foreign key while having them ignored
on a MySQL backend, use a custom compile rule::

    from sqlalchemy.ext.compiler import compiles
    from sqlalchemy.schema import ForeignKeyConstraint

    @compiles(ForeignKeyConstraint, "mysql")
    def process(element, compiler, **kw):
        element.deferrable = element.initially = None
        return compiler.visit_foreign_key_constraint(element, **kw)

.. versionchanged:: 0.8.3 - the MySQL backend will emit a warning when the
   the ``deferrable`` or ``initially`` keyword arguments of :class:`.ForeignKeyConstraint`
   and :class:`.ForeignKey` are used.  The arguments will no longer be
   ignored in 0.9.

The "MATCH" keyword is in fact more insidious, and in a future release will be
explicitly disallowed
by SQLAlchemy in conjunction with the MySQL backend.  This argument is silently
ignored by MySQL, but in addition has the effect of ON UPDATE and ON DELETE options
also being ignored by the backend.   Therefore MATCH should never be used with the
MySQL backend; as is the case with DEFERRABLE and INITIALLY, custom compilation
rules can be used to correct a MySQL ForeignKeyConstraint at DDL definition time.

.. versionadded:: 0.8.3 - the MySQL backend will emit a warning when
   the ``match`` keyword is used with :class:`.ForeignKeyConstraint`
   or :class:`.ForeignKey`.  This will be a :class:`.CompileError` in 0.9.

Reflection of Foreign Key Constraints
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Not all MySQL storage engines support foreign keys.  When using the
very common ``MyISAM`` MySQL storage engine, the information loaded by table
reflection will not include foreign keys.  For these tables, you may supply a
:class:`~sqlalchemy.ForeignKeyConstraint` at reflection time::

  Table('mytable', metadata,
        ForeignKeyConstraint(['other_id'], ['othertable.other_id']),
        autoload=True
       )

.. seealso::

    :ref:`mysql_storage_engines`

"""

import datetime
import re
import sys

from ... import schema as sa_schema
from ... import exc, log, sql, util
from ...sql import compiler
from array import array as _array

from ...engine import reflection
from ...engine import default
from ... import types as sqltypes
from ...util import topological
from ...types import DATE, BOOLEAN, \
                                BLOB, BINARY, VARBINARY

RESERVED_WORDS = set(
    ['accessible', 'add', 'all', 'alter', 'analyze', 'and', 'as', 'asc',
     'asensitive', 'before', 'between', 'bigint', 'binary', 'blob', 'both',
     'by', 'call', 'cascade', 'case', 'change', 'char', 'character', 'check',
     'collate', 'column', 'condition', 'constraint', 'continue', 'convert',
     'create', 'cross', 'current_date', 'current_time', 'current_timestamp',
     'current_user', 'cursor', 'database', 'databases', 'day_hour',
     'day_microsecond', 'day_minute', 'day_second', 'dec', 'decimal',
     'declare', 'default', 'delayed', 'delete', 'desc', 'describe',
     'deterministic', 'distinct', 'distinctrow', 'div', 'double', 'drop',
     'dual', 'each', 'else', 'elseif', 'enclosed', 'escaped', 'exists',
     'exit', 'explain', 'false', 'fetch', 'float', 'float4', 'float8',
     'for', 'force', 'foreign', 'from', 'fulltext', 'grant', 'group', 'having',
     'high_priority', 'hour_microsecond', 'hour_minute', 'hour_second', 'if',
     'ignore', 'in', 'index', 'infile', 'inner', 'inout', 'insensitive',
     'insert', 'int', 'int1', 'int2', 'int3', 'int4', 'int8', 'integer',
     'interval', 'into', 'is', 'iterate', 'join', 'key', 'keys', 'kill',
     'leading', 'leave', 'left', 'like', 'limit', 'linear', 'lines', 'load',
     'localtime', 'localtimestamp', 'lock', 'long', 'longblob', 'longtext',
     'loop', 'low_priority', 'master_ssl_verify_server_cert', 'match',
     'mediumblob', 'mediumint', 'mediumtext', 'middleint',
     'minute_microsecond', 'minute_second', 'mod', 'modifies', 'natural',
     'not', 'no_write_to_binlog', 'null', 'numeric', 'on', 'optimize',
     'option', 'optionally', 'or', 'order', 'out', 'outer', 'outfile',
     'precision', 'primary', 'procedure', 'purge', 'range', 'read', 'reads',
     'read_only', 'read_write', 'real', 'references', 'regexp', 'release',
     'rename', 'repeat', 'replace', 'require', 'restrict', 'return',
     'revoke', 'right', 'rlike', 'schema', 'schemas', 'second_microsecond',
     'select', 'sensitive', 'separator', 'set', 'show', 'smallint', 'spatial',
     'specific', 'sql', 'sqlexception', 'sqlstate', 'sqlwarning',
     'sql_big_result', 'sql_calc_found_rows', 'sql_small_result', 'ssl',
     'starting', 'straight_join', 'table', 'terminated', 'then', 'tinyblob',
     'tinyint', 'tinytext', 'to', 'trailing', 'trigger', 'true', 'undo',
     'union', 'unique', 'unlock', 'unsigned', 'update', 'usage', 'use',
     'using', 'utc_date', 'utc_time', 'utc_timestamp', 'values', 'varbinary',
     'varchar', 'varcharacter', 'varying', 'when', 'where', 'while', 'with',

     'write', 'x509', 'xor', 'year_month', 'zerofill',  # 5.0

     'columns', 'fields', 'privileges', 'soname', 'tables',  # 4.1

     'accessible', 'linear', 'master_ssl_verify_server_cert', 'range',
     'read_only', 'read_write',  # 5.1

     'general', 'ignore_server_ids', 'master_heartbeat_period', 'maxvalue',
     'resignal', 'signal', 'slow', # 5.5

      'get', 'io_after_gtids', 'io_before_gtids', 'master_bind', 'one_shot',
        'partition', 'sql_after_gtids', 'sql_before_gtids',  # 5.6

     ])

AUTOCOMMIT_RE = re.compile(
    r'\s*(?:UPDATE|INSERT|CREATE|DELETE|DROP|ALTER|LOAD +DATA|REPLACE)',
    re.I | re.UNICODE)
SET_RE = re.compile(
    r'\s*SET\s+(?:(?:GLOBAL|SESSION)\s+)?\w',
    re.I | re.UNICODE)


class _NumericType(object):
    """Base for MySQL numeric types."""

    def __init__(self, unsigned=False, zerofill=False, **kw):
        self.unsigned = unsigned
        self.zerofill = zerofill
        super(_NumericType, self).__init__(**kw)


class _FloatType(_NumericType, sqltypes.Float):
    def __init__(self, precision=None, scale=None, asdecimal=True, **kw):
        if isinstance(self, (REAL, DOUBLE)) and \
            (
                (precision is None and scale is not None) or
                (precision is not None and scale is None)
            ):
            raise exc.ArgumentError(
                "You must specify both precision and scale or omit "
                "both altogether.")

        super(_FloatType, self).__init__(precision=precision, asdecimal=asdecimal, **kw)
        self.scale = scale


class _IntegerType(_NumericType, sqltypes.Integer):
    def __init__(self, display_width=None, **kw):
        self.display_width = display_width
        super(_IntegerType, self).__init__(**kw)


class _StringType(sqltypes.String):
    """Base for MySQL string types."""

    def __init__(self, charset=None, collation=None,
                 ascii=False, binary=False,
                 national=False, **kw):
        self.charset = charset

        # allow collate= or collation=
        kw.setdefault('collation', kw.pop('collate', collation))

        self.ascii = ascii
        # We have to munge the 'unicode' param strictly as a dict
        # otherwise 2to3 will turn it into str.
        self.__dict__['unicode'] = kw.get('unicode', False)
        # sqltypes.String does not accept the 'unicode' arg at all.
        if 'unicode' in kw:
            del kw['unicode']
        self.binary = binary
        self.national = national
        super(_StringType, self).__init__(**kw)


class NUMERIC(_NumericType, sqltypes.NUMERIC):
    """MySQL NUMERIC type."""

    __visit_name__ = 'NUMERIC'

    def __init__(self, precision=None, scale=None, asdecimal=True, **kw):
        """Construct a NUMERIC.

        :param precision: Total digits in this number.  If scale and precision
          are both None, values are stored to limits allowed by the server.

        :param scale: The number of digits after the decimal point.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(NUMERIC, self).__init__(precision=precision,
                                scale=scale, asdecimal=asdecimal, **kw)


class DECIMAL(_NumericType, sqltypes.DECIMAL):
    """MySQL DECIMAL type."""

    __visit_name__ = 'DECIMAL'

    def __init__(self, precision=None, scale=None, asdecimal=True, **kw):
        """Construct a DECIMAL.

        :param precision: Total digits in this number.  If scale and precision
          are both None, values are stored to limits allowed by the server.

        :param scale: The number of digits after the decimal point.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(DECIMAL, self).__init__(precision=precision, scale=scale,
                                      asdecimal=asdecimal, **kw)


class DOUBLE(_FloatType):
    """MySQL DOUBLE type."""

    __visit_name__ = 'DOUBLE'

    def __init__(self, precision=None, scale=None, asdecimal=True, **kw):
        """Construct a DOUBLE.

        :param precision: Total digits in this number.  If scale and precision
          are both None, values are stored to limits allowed by the server.

        :param scale: The number of digits after the decimal point.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(DOUBLE, self).__init__(precision=precision, scale=scale,
                                     asdecimal=asdecimal, **kw)


class REAL(_FloatType, sqltypes.REAL):
    """MySQL REAL type."""

    __visit_name__ = 'REAL'

    def __init__(self, precision=None, scale=None, asdecimal=True, **kw):
        """Construct a REAL.

        :param precision: Total digits in this number.  If scale and precision
          are both None, values are stored to limits allowed by the server.

        :param scale: The number of digits after the decimal point.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(REAL, self).__init__(precision=precision, scale=scale,
                                   asdecimal=asdecimal, **kw)


class FLOAT(_FloatType, sqltypes.FLOAT):
    """MySQL FLOAT type."""

    __visit_name__ = 'FLOAT'

    def __init__(self, precision=None, scale=None, asdecimal=False, **kw):
        """Construct a FLOAT.

        :param precision: Total digits in this number.  If scale and precision
          are both None, values are stored to limits allowed by the server.

        :param scale: The number of digits after the decimal point.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(FLOAT, self).__init__(precision=precision, scale=scale,
                                    asdecimal=asdecimal, **kw)

    def bind_processor(self, dialect):
        return None


class INTEGER(_IntegerType, sqltypes.INTEGER):
    """MySQL INTEGER type."""

    __visit_name__ = 'INTEGER'

    def __init__(self, display_width=None, **kw):
        """Construct an INTEGER.

        :param display_width: Optional, maximum display width for this number.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(INTEGER, self).__init__(display_width=display_width, **kw)


class BIGINT(_IntegerType, sqltypes.BIGINT):
    """MySQL BIGINTEGER type."""

    __visit_name__ = 'BIGINT'

    def __init__(self, display_width=None, **kw):
        """Construct a BIGINTEGER.

        :param display_width: Optional, maximum display width for this number.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(BIGINT, self).__init__(display_width=display_width, **kw)


class MEDIUMINT(_IntegerType):
    """MySQL MEDIUMINTEGER type."""

    __visit_name__ = 'MEDIUMINT'

    def __init__(self, display_width=None, **kw):
        """Construct a MEDIUMINTEGER

        :param display_width: Optional, maximum display width for this number.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(MEDIUMINT, self).__init__(display_width=display_width, **kw)


class TINYINT(_IntegerType):
    """MySQL TINYINT type."""

    __visit_name__ = 'TINYINT'

    def __init__(self, display_width=None, **kw):
        """Construct a TINYINT.

        :param display_width: Optional, maximum display width for this number.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(TINYINT, self).__init__(display_width=display_width, **kw)


class SMALLINT(_IntegerType, sqltypes.SMALLINT):
    """MySQL SMALLINTEGER type."""

    __visit_name__ = 'SMALLINT'

    def __init__(self, display_width=None, **kw):
        """Construct a SMALLINTEGER.

        :param display_width: Optional, maximum display width for this number.

        :param unsigned: a boolean, optional.

        :param zerofill: Optional. If true, values will be stored as strings
          left-padded with zeros. Note that this does not effect the values
          returned by the underlying database API, which continue to be
          numeric.

        """
        super(SMALLINT, self).__init__(display_width=display_width, **kw)


class BIT(sqltypes.TypeEngine):
    """MySQL BIT type.

    This type is for MySQL 5.0.3 or greater for MyISAM, and 5.0.5 or greater for
    MyISAM, MEMORY, InnoDB and BDB.  For older versions, use a MSTinyInteger()
    type.

    """

    __visit_name__ = 'BIT'

    def __init__(self, length=None):
        """Construct a BIT.

        :param length: Optional, number of bits.

        """
        self.length = length

    def result_processor(self, dialect, coltype):
        """Convert a MySQL's 64 bit, variable length binary string to a long.

        TODO: this is MySQL-db, pyodbc specific.  OurSQL and mysqlconnector
        already do this, so this logic should be moved to those dialects.

        """

        def process(value):
            if value is not None:
                v = 0L
                for i in map(ord, value):
                    v = v << 8 | i
                return v
            return value
        return process


class TIME(sqltypes.TIME):
    """MySQL TIME type. """

    __visit_name__ = 'TIME'

    def __init__(self, timezone=False, fsp=None):
        """Construct a MySQL TIME type.

        :param timezone: not used by the MySQL dialect.
        :param fsp: fractional seconds precision value.
         MySQL 5.6 supports storage of fractional seconds;
         this parameter will be used when emitting DDL
         for the TIME type.

         .. note::

            DBAPI driver support for fractional seconds may
            be limited; current support includes
            MySQL Connector/Python.

        .. versionadded:: 0.8 The MySQL-specific TIME
           type as well as fractional seconds support.

        """
        super(TIME, self).__init__(timezone=timezone)
        self.fsp = fsp

    def result_processor(self, dialect, coltype):
        time = datetime.time

        def process(value):
            # convert from a timedelta value
            if value is not None:
                microseconds = value.microseconds
                seconds = value.seconds
                minutes = seconds // 60
                return time(minutes // 60,
                            minutes % 60,
                            seconds - minutes * 60,
                            microsecond=microseconds)
            else:
                return None
        return process


class TIMESTAMP(sqltypes.TIMESTAMP):
    """MySQL TIMESTAMP type.

    """

    __visit_name__ = 'TIMESTAMP'

    def __init__(self, timezone=False, fsp=None):
        """Construct a MySQL TIMESTAMP type.

        :param timezone: not used by the MySQL dialect.
        :param fsp: fractional seconds precision value.
         MySQL 5.6.4 supports storage of fractional seconds;
         this parameter will be used when emitting DDL
         for the TIMESTAMP type.

         .. note::

            DBAPI driver support for fractional seconds may
            be limited; current support includes
            MySQL Connector/Python.

        .. versionadded:: 0.8.5 Added MySQL-specific :class:`.mysql.TIMESTAMP`
           with fractional seconds support.

        """
        super(TIMESTAMP, self).__init__(timezone=timezone)
        self.fsp = fsp


class DATETIME(sqltypes.DATETIME):
    """MySQL DATETIME type.

    """

    __visit_name__ = 'DATETIME'

    def __init__(self, timezone=False, fsp=None):
        """Construct a MySQL DATETIME type.

        :param timezone: not used by the MySQL dialect.
        :param fsp: fractional seconds precision value.
         MySQL 5.6.4 supports storage of fractional seconds;
         this parameter will be used when emitting DDL
         for the DATETIME type.

         .. note::

            DBAPI driver support for fractional seconds may
            be limited; current support includes
            MySQL Connector/Python.

        .. versionadded:: 0.8.5 Added MySQL-specific :class:`.mysql.DATETIME`
           with fractional seconds support.

        """
        super(DATETIME, self).__init__(timezone=timezone)
        self.fsp = fsp


class YEAR(sqltypes.TypeEngine):
    """MySQL YEAR type, for single byte storage of years 1901-2155."""

    __visit_name__ = 'YEAR'

    def __init__(self, display_width=None):
        self.display_width = display_width


class TEXT(_StringType, sqltypes.TEXT):
    """MySQL TEXT type, for text up to 2^16 characters."""

    __visit_name__ = 'TEXT'

    def __init__(self, length=None, **kw):
        """Construct a TEXT.

        :param length: Optional, if provided the server may optimize storage
          by substituting the smallest TEXT type sufficient to store
          ``length`` characters.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param national: Optional. If true, use the server's configured
          national character set.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        super(TEXT, self).__init__(length=length, **kw)


class TINYTEXT(_StringType):
    """MySQL TINYTEXT type, for text up to 2^8 characters."""

    __visit_name__ = 'TINYTEXT'

    def __init__(self, **kwargs):
        """Construct a TINYTEXT.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param national: Optional. If true, use the server's configured
          national character set.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        super(TINYTEXT, self).__init__(**kwargs)


class MEDIUMTEXT(_StringType):
    """MySQL MEDIUMTEXT type, for text up to 2^24 characters."""

    __visit_name__ = 'MEDIUMTEXT'

    def __init__(self, **kwargs):
        """Construct a MEDIUMTEXT.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param national: Optional. If true, use the server's configured
          national character set.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        super(MEDIUMTEXT, self).__init__(**kwargs)


class LONGTEXT(_StringType):
    """MySQL LONGTEXT type, for text up to 2^32 characters."""

    __visit_name__ = 'LONGTEXT'

    def __init__(self, **kwargs):
        """Construct a LONGTEXT.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param national: Optional. If true, use the server's configured
          national character set.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        super(LONGTEXT, self).__init__(**kwargs)


class VARCHAR(_StringType, sqltypes.VARCHAR):
    """MySQL VARCHAR type, for variable-length character data."""

    __visit_name__ = 'VARCHAR'

    def __init__(self, length=None, **kwargs):
        """Construct a VARCHAR.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param national: Optional. If true, use the server's configured
          national character set.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        super(VARCHAR, self).__init__(length=length, **kwargs)


class CHAR(_StringType, sqltypes.CHAR):
    """MySQL CHAR type, for fixed-length character data."""

    __visit_name__ = 'CHAR'

    def __init__(self, length=None, **kwargs):
        """Construct a CHAR.

        :param length: Maximum data length, in characters.

        :param binary: Optional, use the default binary collation for the
          national character set.  This does not affect the type of data
          stored, use a BINARY type for binary data.

        :param collation: Optional, request a particular collation.  Must be
          compatible with the national character set.

        """
        super(CHAR, self).__init__(length=length, **kwargs)


class NVARCHAR(_StringType, sqltypes.NVARCHAR):
    """MySQL NVARCHAR type.

    For variable-length character data in the server's configured national
    character set.
    """

    __visit_name__ = 'NVARCHAR'

    def __init__(self, length=None, **kwargs):
        """Construct an NVARCHAR.

        :param length: Maximum data length, in characters.

        :param binary: Optional, use the default binary collation for the
          national character set.  This does not affect the type of data
          stored, use a BINARY type for binary data.

        :param collation: Optional, request a particular collation.  Must be
          compatible with the national character set.

        """
        kwargs['national'] = True
        super(NVARCHAR, self).__init__(length=length, **kwargs)


class NCHAR(_StringType, sqltypes.NCHAR):
    """MySQL NCHAR type.

    For fixed-length character data in the server's configured national
    character set.
    """

    __visit_name__ = 'NCHAR'

    def __init__(self, length=None, **kwargs):
        """Construct an NCHAR.

        :param length: Maximum data length, in characters.

        :param binary: Optional, use the default binary collation for the
          national character set.  This does not affect the type of data
          stored, use a BINARY type for binary data.

        :param collation: Optional, request a particular collation.  Must be
          compatible with the national character set.

        """
        kwargs['national'] = True
        super(NCHAR, self).__init__(length=length, **kwargs)


class TINYBLOB(sqltypes._Binary):
    """MySQL TINYBLOB type, for binary data up to 2^8 bytes."""

    __visit_name__ = 'TINYBLOB'


class MEDIUMBLOB(sqltypes._Binary):
    """MySQL MEDIUMBLOB type, for binary data up to 2^24 bytes."""

    __visit_name__ = 'MEDIUMBLOB'


class LONGBLOB(sqltypes._Binary):
    """MySQL LONGBLOB type, for binary data up to 2^32 bytes."""

    __visit_name__ = 'LONGBLOB'


class ENUM(sqltypes.Enum, _StringType):
    """MySQL ENUM type."""

    __visit_name__ = 'ENUM'

    def __init__(self, *enums, **kw):
        """Construct an ENUM.

        Example:

          Column('myenum', MSEnum("foo", "bar", "baz"))

        :param enums: The range of valid values for this ENUM.  Values will be
          quoted when generating the schema according to the quoting flag (see
          below).

        :param strict: Defaults to False: ensure that a given value is in this
          ENUM's range of permissible values when inserting or updating rows.
          Note that MySQL will not raise a fatal error if you attempt to store
          an out of range value- an alternate value will be stored instead.
          (See MySQL ENUM documentation.)

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        :param quoting: Defaults to 'auto': automatically determine enum value
          quoting.  If all enum values are surrounded by the same quoting
          character, then use 'quoted' mode.  Otherwise, use 'unquoted' mode.

          'quoted': values in enums are already quoted, they will be used
          directly when generating the schema - this usage is deprecated.

          'unquoted': values in enums are not quoted, they will be escaped and
          surrounded by single quotes when generating the schema.

          Previous versions of this type always required manually quoted
          values to be supplied; future versions will always quote the string
          literals for you.  This is a transitional option.

        """
        self.quoting = kw.pop('quoting', 'auto')

        if self.quoting == 'auto' and len(enums):
            # What quoting character are we using?
            q = None
            for e in enums:
                if len(e) == 0:
                    self.quoting = 'unquoted'
                    break
                elif q is None:
                    q = e[0]

                if e[0] != q or e[-1] != q:
                    self.quoting = 'unquoted'
                    break
            else:
                self.quoting = 'quoted'

        if self.quoting == 'quoted':
            util.warn_deprecated(
                'Manually quoting ENUM value literals is deprecated.  Supply '
                'unquoted values and use the quoting= option in cases of '
                'ambiguity.')
            enums = self._strip_enums(enums)

        self.strict = kw.pop('strict', False)
        length = max([len(v) for v in enums] + [0])
        kw.pop('metadata', None)
        kw.pop('schema', None)
        kw.pop('name', None)
        kw.pop('quote', None)
        kw.pop('native_enum', None)
        kw.pop('inherit_schema', None)
        _StringType.__init__(self, length=length, **kw)
        sqltypes.Enum.__init__(self, *enums)

    @classmethod
    def _strip_enums(cls, enums):
        strip_enums = []
        for a in enums:
            if a[0:1] == '"' or a[0:1] == "'":
                # strip enclosing quotes and unquote interior
                a = a[1:-1].replace(a[0] * 2, a[0])
            strip_enums.append(a)
        return strip_enums

    def bind_processor(self, dialect):
        super_convert = super(ENUM, self).bind_processor(dialect)

        def process(value):
            if self.strict and value is not None and value not in self.enums:
                raise exc.InvalidRequestError('"%s" not a valid value for '
                                                     'this enum' % value)
            if super_convert:
                return super_convert(value)
            else:
                return value
        return process

    def adapt(self, impltype, **kw):
        kw['strict'] = self.strict
        return sqltypes.Enum.adapt(self, impltype, **kw)


class SET(_StringType):
    """MySQL SET type."""

    __visit_name__ = 'SET'

    def __init__(self, *values, **kw):
        """Construct a SET.

        Example::

          Column('myset', MSSet("'foo'", "'bar'", "'baz'"))

        :param values: The range of valid values for this SET.  Values will be
          used exactly as they appear when generating schemas.  Strings must
          be quoted, as in the example above.  Single-quotes are suggested for
          ANSI compatibility and are required for portability to servers with
          ANSI_QUOTES enabled.

        :param charset: Optional, a column-level character set for this string
          value.  Takes precedence to 'ascii' or 'unicode' short-hand.

        :param collation: Optional, a column-level collation for this string
          value.  Takes precedence to 'binary' short-hand.

        :param ascii: Defaults to False: short-hand for the ``latin1``
          character set, generates ASCII in schema.

        :param unicode: Defaults to False: short-hand for the ``ucs2``
          character set, generates UNICODE in schema.

        :param binary: Defaults to False: short-hand, pick the binary
          collation type that matches the column's character set.  Generates
          BINARY in schema.  This does not affect the type of data stored,
          only the collation of character data.

        """
        self._ddl_values = values

        strip_values = []
        for a in values:
            if a[0:1] == '"' or a[0:1] == "'":
                # strip enclosing quotes and unquote interior
                a = a[1:-1].replace(a[0] * 2, a[0])
            strip_values.append(a)

        self.values = strip_values
        kw.setdefault('length', max([len(v) for v in strip_values] + [0]))
        super(SET, self).__init__(**kw)

    def result_processor(self, dialect, coltype):
        def process(value):
            # The good news:
            #   No ',' quoting issues- commas aren't allowed in SET values
            # The bad news:
            #   Plenty of driver inconsistencies here.
            if isinstance(value, util.set_types):
                # ..some versions convert '' to an empty set
                if not value:
                    value.add('')
                # ..some return sets.Set, even for pythons
                # that have __builtin__.set
                if not isinstance(value, set):
                    value = set(value)
                return value
            # ...and some versions return strings
            if value is not None:
                return set(value.split(','))
            else:
                return value
        return process

    def bind_processor(self, dialect):
        super_convert = super(SET, self).bind_processor(dialect)

        def process(value):
            if value is None or isinstance(value, (int, long, basestring)):
                pass
            else:
                if None in value:
                    value = set(value)
                    value.remove(None)
                    value.add('')
                value = ','.join(value)
            if super_convert:
                return super_convert(value)
            else:
                return value
        return process

# old names
MSTime = TIME
MSSet = SET
MSEnum = ENUM
MSLongBlob = LONGBLOB
MSMediumBlob = MEDIUMBLOB
MSTinyBlob = TINYBLOB
MSBlob = BLOB
MSBinary = BINARY
MSVarBinary = VARBINARY
MSNChar = NCHAR
MSNVarChar = NVARCHAR
MSChar = CHAR
MSString = VARCHAR
MSLongText = LONGTEXT
MSMediumText = MEDIUMTEXT
MSTinyText = TINYTEXT
MSText = TEXT
MSYear = YEAR
MSTimeStamp = TIMESTAMP
MSBit = BIT
MSSmallInteger = SMALLINT
MSTinyInteger = TINYINT
MSMediumInteger = MEDIUMINT
MSBigInteger = BIGINT
MSNumeric = NUMERIC
MSDecimal = DECIMAL
MSDouble = DOUBLE
MSReal = REAL
MSFloat = FLOAT
MSInteger = INTEGER

colspecs = {
    sqltypes.Numeric: NUMERIC,
    sqltypes.Float: FLOAT,
    sqltypes.Time: TIME,
    sqltypes.Enum: ENUM,
}

# Everything 3.23 through 5.1 excepting OpenGIS types.
ischema_names = {
    'bigint': BIGINT,
    'binary': BINARY,
    'bit': BIT,
    'blob': BLOB,
    'boolean': BOOLEAN,
    'char': CHAR,
    'date': DATE,
    'datetime': DATETIME,
    'decimal': DECIMAL,
    'double': DOUBLE,
    'enum': ENUM,
    'fixed': DECIMAL,
    'float': FLOAT,
    'int': INTEGER,
    'integer': INTEGER,
    'longblob': LONGBLOB,
    'longtext': LONGTEXT,
    'mediumblob': MEDIUMBLOB,
    'mediumint': MEDIUMINT,
    'mediumtext': MEDIUMTEXT,
    'nchar': NCHAR,
    'nvarchar': NVARCHAR,
    'numeric': NUMERIC,
    'set': SET,
    'smallint': SMALLINT,
    'text': TEXT,
    'time': TIME,
    'timestamp': TIMESTAMP,
    'tinyblob': TINYBLOB,
    'tinyint': TINYINT,
    'tinytext': TINYTEXT,
    'varbinary': VARBINARY,
    'varchar': VARCHAR,
    'year': YEAR,
}


class MySQLExecutionContext(default.DefaultExecutionContext):

    def should_autocommit_text(self, statement):
        return AUTOCOMMIT_RE.match(statement)


class MySQLCompiler(compiler.SQLCompiler):

    render_table_with_column_in_update_from = True
    """Overridden from base SQLCompiler value"""

    extract_map = compiler.SQLCompiler.extract_map.copy()
    extract_map.update({'milliseconds': 'millisecond'})

    def visit_random_func(self, fn, **kw):
        return "rand%s" % self.function_argspec(fn)

    def visit_utc_timestamp_func(self, fn, **kw):
        return "UTC_TIMESTAMP"

    def visit_sysdate_func(self, fn, **kw):
        return "SYSDATE()"

    def visit_concat_op_binary(self, binary, operator, **kw):
        return "concat(%s, %s)" % (self.process(binary.left),
                                                self.process(binary.right))

    def visit_match_op_binary(self, binary, operator, **kw):
        return "MATCH (%s) AGAINST (%s IN BOOLEAN MODE)" % \
                    (self.process(binary.left), self.process(binary.right))

    def get_from_hint_text(self, table, text):
        return text

    def visit_typeclause(self, typeclause):
        type_ = typeclause.type.dialect_impl(self.dialect)
        if isinstance(type_, sqltypes.Integer):
            if getattr(type_, 'unsigned', False):
                return 'UNSIGNED INTEGER'
            else:
                return 'SIGNED INTEGER'
        elif isinstance(type_, sqltypes.TIMESTAMP):
            return 'DATETIME'
        elif isinstance(type_, (sqltypes.DECIMAL, sqltypes.DateTime,
                                            sqltypes.Date, sqltypes.Time)):
            return self.dialect.type_compiler.process(type_)
        elif isinstance(type_, sqltypes.Text):
            return 'CHAR'
        elif (isinstance(type_, sqltypes.String) and not
              isinstance(type_, (ENUM, SET))):
            if getattr(type_, 'length'):
                return 'CHAR(%s)' % type_.length
            else:
                return 'CHAR'
        elif isinstance(type_, sqltypes._Binary):
            return 'BINARY'
        elif isinstance(type_, sqltypes.NUMERIC):
            return self.dialect.type_compiler.process(
                                        type_).replace('NUMERIC', 'DECIMAL')
        else:
            return None

    def visit_cast(self, cast, **kwargs):
        # No cast until 4, no decimals until 5.
        if not self.dialect._supports_cast:
            return self.process(cast.clause.self_group())

        type_ = self.process(cast.typeclause)
        if type_ is None:
            return self.process(cast.clause.self_group())

        return 'CAST(%s AS %s)' % (self.process(cast.clause), type_)

    def render_literal_value(self, value, type_):
        value = super(MySQLCompiler, self).render_literal_value(value, type_)
        if self.dialect._backslash_escapes:
            value = value.replace('\\', '\\\\')
        return value

    def get_select_precolumns(self, select):
        """Add special MySQL keywords in place of DISTINCT.

        .. note::

          this usage is deprecated.  :meth:`.Select.prefix_with`
          should be used for special keywords at the start
          of a SELECT.

        """
        if isinstance(select._distinct, basestring):
            return select._distinct.upper() + " "
        elif select._distinct:
            return "DISTINCT "
        else:
            return ""

    def visit_join(self, join, asfrom=False, **kwargs):
        # 'JOIN ... ON ...' for inner joins isn't available until 4.0.
        # Apparently < 3.23.17 requires theta joins for inner joins
        # (but not outer).  Not generating these currently, but
        # support can be added, preferably after dialects are
        # refactored to be version-sensitive.
        return ''.join(
            (self.process(join.left, asfrom=True, **kwargs),
             (join.isouter and " LEFT OUTER JOIN " or " INNER JOIN "),
             self.process(join.right, asfrom=True, **kwargs),
             " ON ",
             self.process(join.onclause, **kwargs)))

    def for_update_clause(self, select):
        if select.for_update == 'read':
            return ' LOCK IN SHARE MODE'
        else:
            return super(MySQLCompiler, self).for_update_clause(select)

    def limit_clause(self, select):
        # MySQL supports:
        #   LIMIT <limit>
        #   LIMIT <offset>, <limit>
        # and in server versions > 3.3:
        #   LIMIT <limit> OFFSET <offset>
        # The latter is more readable for offsets but we're stuck with the
        # former until we can refine dialects by server revision.

        limit, offset = select._limit, select._offset

        if (limit, offset) == (None, None):
            return ''
        elif offset is not None:
            # As suggested by the MySQL docs, need to apply an
            # artificial limit if one wasn't provided
            # http://dev.mysql.com/doc/refman/5.0/en/select.html
            if limit is None:
                # hardwire the upper limit.  Currently
                # needed by OurSQL with Python 3
                # (https://bugs.launchpad.net/oursql/+bug/686232),
                # but also is consistent with the usage of the upper
                # bound as part of MySQL's "syntax" for OFFSET with
                # no LIMIT
                return ' \n LIMIT %s, %s' % (
                                self.process(sql.literal(offset)),
                                "18446744073709551615")
            else:
                return ' \n LIMIT %s, %s' % (
                                self.process(sql.literal(offset)),
                                self.process(sql.literal(limit)))
        else:
            # No offset provided, so just use the limit
            return ' \n LIMIT %s' % (self.process(sql.literal(limit)),)

    def update_limit_clause(self, update_stmt):
        limit = update_stmt.kwargs.get('%s_limit' % self.dialect.name, None)
        if limit:
            return "LIMIT %s" % limit
        else:
            return None

    def update_tables_clause(self, update_stmt, from_table, extra_froms, **kw):
        return ', '.join(t._compiler_dispatch(self, asfrom=True, **kw)
                    for t in [from_table] + list(extra_froms))

    def update_from_clause(self, update_stmt, from_table,
                                extra_froms, from_hints, **kw):
        return None


# ug.  "InnoDB needs indexes on foreign keys and referenced keys [...].
#       Starting with MySQL 4.1.2, these indexes are created automatically.
#       In older versions, the indexes must be created explicitly or the
#       creation of foreign key constraints fails."

class MySQLDDLCompiler(compiler.DDLCompiler):
    def create_table_constraints(self, table):
        """Get table constraints."""
        constraint_string = super(
                        MySQLDDLCompiler, self).create_table_constraints(table)

        engine_key = '%s_engine' % self.dialect.name
        is_innodb = table.kwargs.has_key(engine_key) and \
                    table.kwargs[engine_key].lower() == 'innodb'

        auto_inc_column = table._autoincrement_column

        if is_innodb and \
                auto_inc_column is not None and \
                auto_inc_column is not list(table.primary_key)[0]:
            if constraint_string:
                constraint_string += ", \n\t"
            constraint_string += "KEY %s (%s)" % (
                        self.preparer.quote(
                            "idx_autoinc_%s" % auto_inc_column.name, None
                        ),
                        self.preparer.format_column(auto_inc_column)
                    )

        return constraint_string

    def get_column_specification(self, column, **kw):
        """Builds column DDL."""

        colspec = [self.preparer.format_column(column),
                    self.dialect.type_compiler.process(column.type)
                   ]

        default = self.get_column_default_string(column)
        if default is not None:
            colspec.append('DEFAULT ' + default)

        is_timestamp = isinstance(column.type, sqltypes.TIMESTAMP)
        if not column.nullable and not is_timestamp:
            colspec.append('NOT NULL')

        elif column.nullable and is_timestamp and default is None:
            colspec.append('NULL')

        if column is column.table._autoincrement_column and \
                    column.server_default is None:
            colspec.append('AUTO_INCREMENT')

        return ' '.join(colspec)

    def post_create_table(self, table):
        """Build table-level CREATE options like ENGINE and COLLATE."""

        table_opts = []

        opts = dict(
            (
                k[len(self.dialect.name) + 1:].upper(),
                v
            )
            for k, v in table.kwargs.items()
            if k.startswith('%s_' % self.dialect.name)
        )

        for opt in topological.sort([
            ('DEFAULT_CHARSET', 'COLLATE'),
            ('DEFAULT_CHARACTER_SET', 'COLLATE'),
            ('PARTITION_BY', 'PARTITIONS'),  # only for test consistency
        ], opts):
            arg = opts[opt]
            if opt in _options_of_type_string:
                arg = "'%s'" % arg.replace("\\", "\\\\").replace("'", "''")

            if opt in ('DATA_DIRECTORY', 'INDEX_DIRECTORY',
                       'DEFAULT_CHARACTER_SET', 'CHARACTER_SET',
                       'DEFAULT_CHARSET',
                       'DEFAULT_COLLATE', 'PARTITION_BY'):
                opt = opt.replace('_', ' ')

            joiner = '='
            if opt in ('TABLESPACE', 'DEFAULT CHARACTER SET',
                       'CHARACTER SET', 'COLLATE', 'PARTITION BY', 'PARTITIONS'):
                joiner = ' '

            table_opts.append(joiner.join((opt, arg)))
        return ' '.join(table_opts)

    def visit_create_index(self, create):
        index = create.element
        self._verify_index_table(index)
        preparer = self.preparer
        table = preparer.format_table(index.table)
        columns = [self.sql_compiler.process(expr, include_table=False,
                        literal_binds=True)
                for expr in index.expressions]

        name = self._prepared_index_name(index)

        text = "CREATE "
        if index.unique:
            text += "UNIQUE "
        text += "INDEX %s ON %s " % (name, table)

        if 'mysql_length' in index.kwargs:
            length = index.kwargs['mysql_length']

            if isinstance(length, dict):
                # length value can be a (column_name --> integer value) mapping
                # specifying the prefix length for each column of the index
                columns = ', '.join(
                    '%s(%d)' % (expr, length[col.name]) if col.name in length
                    else
                    (
                        '%s(%d)' % (expr, length[expr]) if expr in length
                        else '%s' % expr
                    )
                    for col, expr in zip(index.expressions, columns)
                )
            else:
                # or can be an integer value specifying the same
                # prefix length for all columns of the index
                columns = ', '.join(
                    '%s(%d)' % (col, length)
                    for col in columns
                )
        else:
            columns = ', '.join(columns)
        text += '(%s)' % columns

        if 'mysql_using' in index.kwargs:
            using = index.kwargs['mysql_using']
            text += " USING %s" % (preparer.quote(using, index.quote))

        return text

    def visit_primary_key_constraint(self, constraint):
        text = super(MySQLDDLCompiler, self).\
            visit_primary_key_constraint(constraint)
        if "mysql_using" in constraint.kwargs:
            using = constraint.kwargs['mysql_using']
            text += " USING %s" % (
                self.preparer.quote(using, constraint.quote))
        return text

    def visit_drop_index(self, drop):
        index = drop.element

        return "\nDROP INDEX %s ON %s" % (
                    self._prepared_index_name(index,
                                        include_schema=False),
                     self.preparer.format_table(index.table))

    def visit_drop_constraint(self, drop):
        constraint = drop.element
        if isinstance(constraint, sa_schema.ForeignKeyConstraint):
            qual = "FOREIGN KEY "
            const = self.preparer.format_constraint(constraint)
        elif isinstance(constraint, sa_schema.PrimaryKeyConstraint):
            qual = "PRIMARY KEY "
            const = ""
        elif isinstance(constraint, sa_schema.UniqueConstraint):
            qual = "INDEX "
            const = self.preparer.format_constraint(constraint)
        else:
            qual = ""
            const = self.preparer.format_constraint(constraint)
        return "ALTER TABLE %s DROP %s%s" % \
                    (self.preparer.format_table(constraint.table),
                    qual, const)

    def define_constraint_deferrability(self, constraint):
        if constraint.deferrable is not None:
            util.warn("The 'deferrable' keyword will no longer be ignored by the "
                "MySQL backend in 0.9 - please adjust so that this keyword is "
                "not used in conjunction with MySQL.")
        if constraint.initially is not None:
            util.warn("The 'initially' keyword will no longer be ignored by the "
                "MySQL backend in 0.9 - please adjust so that this keyword is "
                "not used in conjunction with MySQL.")

        return ""


    def define_constraint_match(self, constraint):
        if constraint.match is not None:
            util.warn("MySQL ignores the 'MATCH' keyword while at the same time "
                    "causes ON UPDATE/ON DELETE clauses to be ignored - "
                    "this will be an exception in 0.9.")
        return ""

class MySQLTypeCompiler(compiler.GenericTypeCompiler):
    def _extend_numeric(self, type_, spec):
        "Extend a numeric-type declaration with MySQL specific extensions."

        if not self._mysql_type(type_):
            return spec

        if type_.unsigned:
            spec += ' UNSIGNED'
        if type_.zerofill:
            spec += ' ZEROFILL'
        return spec

    def _extend_string(self, type_, defaults, spec):
        """Extend a string-type declaration with standard SQL CHARACTER SET /
        COLLATE annotations and MySQL specific extensions.

        """

        def attr(name):
            return getattr(type_, name, defaults.get(name))

        if attr('charset'):
            charset = 'CHARACTER SET %s' % attr('charset')
        elif attr('ascii'):
            charset = 'ASCII'
        elif attr('unicode'):
            charset = 'UNICODE'
        else:
            charset = None

        if attr('collation'):
            collation = 'COLLATE %s' % type_.collation
        elif attr('binary'):
            collation = 'BINARY'
        else:
            collation = None

        if attr('national'):
            # NATIONAL (aka NCHAR/NVARCHAR) trumps charsets.
            return ' '.join([c for c in ('NATIONAL', spec, collation)
                             if c is not None])
        return ' '.join([c for c in (spec, charset, collation)
                         if c is not None])

    def _mysql_type(self, type_):
        return isinstance(type_, (_StringType, _NumericType))

    def visit_NUMERIC(self, type_):
        if type_.precision is None:
            return self._extend_numeric(type_, "NUMERIC")
        elif type_.scale is None:
            return self._extend_numeric(type_,
                            "NUMERIC(%(precision)s)" %
                            {'precision': type_.precision})
        else:
            return self._extend_numeric(type_,
                            "NUMERIC(%(precision)s, %(scale)s)" %
                            {'precision': type_.precision,
                            'scale': type_.scale})

    def visit_DECIMAL(self, type_):
        if type_.precision is None:
            return self._extend_numeric(type_, "DECIMAL")
        elif type_.scale is None:
            return self._extend_numeric(type_,
                            "DECIMAL(%(precision)s)" %
                            {'precision': type_.precision})
        else:
            return self._extend_numeric(type_,
                            "DECIMAL(%(precision)s, %(scale)s)" %
                            {'precision': type_.precision,
                            'scale': type_.scale})

    def visit_DOUBLE(self, type_):
        if type_.precision is not None and type_.scale is not None:
            return self._extend_numeric(type_,
                                "DOUBLE(%(precision)s, %(scale)s)" %
                                {'precision': type_.precision,
                                 'scale': type_.scale})
        else:
            return self._extend_numeric(type_, 'DOUBLE')

    def visit_REAL(self, type_):
        if type_.precision is not None and type_.scale is not None:
            return self._extend_numeric(type_,
                                "REAL(%(precision)s, %(scale)s)" %
                                {'precision': type_.precision,
                                 'scale': type_.scale})
        else:
            return self._extend_numeric(type_, 'REAL')

    def visit_FLOAT(self, type_):
        if self._mysql_type(type_) and \
            type_.scale is not None and \
            type_.precision is not None:
            return self._extend_numeric(type_,
                            "FLOAT(%s, %s)" % (type_.precision, type_.scale))
        elif type_.precision is not None:
            return self._extend_numeric(type_,
                                            "FLOAT(%s)" % (type_.precision,))
        else:
            return self._extend_numeric(type_, "FLOAT")

    def visit_INTEGER(self, type_):
        if self._mysql_type(type_) and type_.display_width is not None:
            return self._extend_numeric(type_,
                        "INTEGER(%(display_width)s)" %
                        {'display_width': type_.display_width})
        else:
            return self._extend_numeric(type_, "INTEGER")

    def visit_BIGINT(self, type_):
        if self._mysql_type(type_) and type_.display_width is not None:
            return self._extend_numeric(type_,
                        "BIGINT(%(display_width)s)" %
                        {'display_width': type_.display_width})
        else:
            return self._extend_numeric(type_, "BIGINT")

    def visit_MEDIUMINT(self, type_):
        if self._mysql_type(type_) and type_.display_width is not None:
            return self._extend_numeric(type_,
                        "MEDIUMINT(%(display_width)s)" %
                        {'display_width': type_.display_width})
        else:
            return self._extend_numeric(type_, "MEDIUMINT")

    def visit_TINYINT(self, type_):
        if self._mysql_type(type_) and type_.display_width is not None:
            return self._extend_numeric(type_,
                                        "TINYINT(%s)" % type_.display_width)
        else:
            return self._extend_numeric(type_, "TINYINT")

    def visit_SMALLINT(self, type_):
        if self._mysql_type(type_) and type_.display_width is not None:
            return self._extend_numeric(type_,
                        "SMALLINT(%(display_width)s)" %
                        {'display_width': type_.display_width}
                    )
        else:
            return self._extend_numeric(type_, "SMALLINT")

    def visit_BIT(self, type_):
        if type_.length is not None:
            return "BIT(%s)" % type_.length
        else:
            return "BIT"

    def visit_DATETIME(self, type_):
        if getattr(type_, 'fsp', None):
            return "DATETIME(%d)" % type_.fsp
        else:
            return "DATETIME"

    def visit_DATE(self, type_):
        return "DATE"

    def visit_TIME(self, type_):
        if getattr(type_, 'fsp', None):
            return "TIME(%d)" % type_.fsp
        else:
            return "TIME"

    def visit_TIMESTAMP(self, type_):
        if getattr(type_, 'fsp', None):
            return "TIMESTAMP(%d)" % type_.fsp
        else:
            return "TIMESTAMP"

    def visit_YEAR(self, type_):
        if type_.display_width is None:
            return "YEAR"
        else:
            return "YEAR(%s)" % type_.display_width

    def visit_TEXT(self, type_):
        if type_.length:
            return self._extend_string(type_, {}, "TEXT(%d)" % type_.length)
        else:
            return self._extend_string(type_, {}, "TEXT")

    def visit_TINYTEXT(self, type_):
        return self._extend_string(type_, {}, "TINYTEXT")

    def visit_MEDIUMTEXT(self, type_):
        return self._extend_string(type_, {}, "MEDIUMTEXT")

    def visit_LONGTEXT(self, type_):
        return self._extend_string(type_, {}, "LONGTEXT")

    def visit_VARCHAR(self, type_):
        if type_.length:
            return self._extend_string(type_, {}, "VARCHAR(%d)" % type_.length)
        else:
            raise exc.CompileError(
                    "VARCHAR requires a length on dialect %s" %
                    self.dialect.name)

    def visit_CHAR(self, type_):
        if type_.length:
            return self._extend_string(type_, {}, "CHAR(%(length)s)" %
                                        {'length': type_.length})
        else:
            return self._extend_string(type_, {}, "CHAR")

    def visit_NVARCHAR(self, type_):
        # We'll actually generate the equiv. "NATIONAL VARCHAR" instead
        # of "NVARCHAR".
        if type_.length:
            return self._extend_string(type_, {'national': True},
                        "VARCHAR(%(length)s)" % {'length': type_.length})
        else:
            raise exc.CompileError(
                    "NVARCHAR requires a length on dialect %s" %
                    self.dialect.name)

    def visit_NCHAR(self, type_):
        # We'll actually generate the equiv.
        # "NATIONAL CHAR" instead of "NCHAR".
        if type_.length:
            return self._extend_string(type_, {'national': True},
                        "CHAR(%(length)s)" % {'length': type_.length})
        else:
            return self._extend_string(type_, {'national': True}, "CHAR")

    def visit_VARBINARY(self, type_):
        return "VARBINARY(%d)" % type_.length

    def visit_large_binary(self, type_):
        return self.visit_BLOB(type_)

    def visit_enum(self, type_):
        if not type_.native_enum:
            return super(MySQLTypeCompiler, self).visit_enum(type_)
        else:
            return self.visit_ENUM(type_)

    def visit_BLOB(self, type_):
        if type_.length:
            return "BLOB(%d)" % type_.length
        else:
            return "BLOB"

    def visit_TINYBLOB(self, type_):
        return "TINYBLOB"

    def visit_MEDIUMBLOB(self, type_):
        return "MEDIUMBLOB"

    def visit_LONGBLOB(self, type_):
        return "LONGBLOB"

    def visit_ENUM(self, type_):
        quoted_enums = []
        for e in type_.enums:
            quoted_enums.append("'%s'" % e.replace("'", "''"))
        return self._extend_string(type_, {}, "ENUM(%s)" %
                                        ",".join(quoted_enums))

    def visit_SET(self, type_):
        return self._extend_string(type_, {}, "SET(%s)" %
                                        ",".join(type_._ddl_values))

    def visit_BOOLEAN(self, type):
        return "BOOL"


class MySQLIdentifierPreparer(compiler.IdentifierPreparer):

    reserved_words = RESERVED_WORDS

    def __init__(self, dialect, server_ansiquotes=False, **kw):
        if not server_ansiquotes:
            quote = "`"
        else:
            quote = '"'

        super(MySQLIdentifierPreparer, self).__init__(
                                                dialect,
                                                initial_quote=quote,
                                                escape_quote=quote)

    def _quote_free_identifiers(self, *ids):
        """Unilaterally identifier-quote any number of strings."""

        return tuple([self.quote_identifier(i) for i in ids if i is not None])


class MySQLDialect(default.DefaultDialect):
    """Details of the MySQL dialect.  Not used directly in application code."""

    name = 'mysql'
    supports_alter = True

    # identifiers are 64, however aliases can be 255...
    max_identifier_length = 255
    max_index_name_length = 64

    supports_native_enum = True

    supports_sane_rowcount = True
    supports_sane_multi_rowcount = False
    supports_multivalues_insert = True

    default_paramstyle = 'format'
    colspecs = colspecs

    statement_compiler = MySQLCompiler
    ddl_compiler = MySQLDDLCompiler
    type_compiler = MySQLTypeCompiler
    ischema_names = ischema_names
    preparer = MySQLIdentifierPreparer

    # default SQL compilation settings -
    # these are modified upon initialize(),
    # i.e. first connect
    _backslash_escapes = True
    _server_ansiquotes = False

    def __init__(self, isolation_level=None, **kwargs):
        kwargs.pop('use_ansiquotes', None)   # legacy
        default.DefaultDialect.__init__(self, **kwargs)
        self.isolation_level = isolation_level

    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 TRANSACTION ISOLATION LEVEL %s" % level)
        cursor.execute("COMMIT")
        cursor.close()

    def get_isolation_level(self, connection):
        cursor = connection.cursor()
        cursor.execute('SELECT @@tx_isolation')
        val = cursor.fetchone()[0]
        cursor.close()
        if util.py3k and isinstance(val, bytes):
            val = val.decode()
        return val.upper().replace("-", " ")

    def do_commit(self, dbapi_connection):
        """Execute a COMMIT."""

        # COMMIT/ROLLBACK were introduced in 3.23.15.
        # Yes, we have at least one user who has to talk to these old versions!
        #
        # Ignore commit/rollback if support isn't present, otherwise even basic
        # operations via autocommit fail.
        try:
            dbapi_connection.commit()
        except:
            if self.server_version_info < (3, 23, 15):
                args = sys.exc_info()[1].args
                if args and args[0] == 1064:
                    return
            raise

    def do_rollback(self, dbapi_connection):
        """Execute a ROLLBACK."""

        try:
            dbapi_connection.rollback()
        except:
            if self.server_version_info < (3, 23, 15):
                args = sys.exc_info()[1].args
                if args and args[0] == 1064:
                    return
            raise

    def do_begin_twophase(self, connection, xid):
        connection.execute(sql.text("XA BEGIN :xid"), xid=xid)

    def do_prepare_twophase(self, connection, xid):
        connection.execute(sql.text("XA END :xid"), xid=xid)
        connection.execute(sql.text("XA PREPARE :xid"), xid=xid)

    def do_rollback_twophase(self, connection, xid, is_prepared=True,
                             recover=False):
        if not is_prepared:
            connection.execute(sql.text("XA END :xid"), xid=xid)
        connection.execute(sql.text("XA ROLLBACK :xid"), xid=xid)

    def do_commit_twophase(self, connection, xid, is_prepared=True,
                           recover=False):
        if not is_prepared:
            self.do_prepare_twophase(connection, xid)
        connection.execute(sql.text("XA COMMIT :xid"), xid=xid)

    def do_recover_twophase(self, connection):
        resultset = connection.execute("XA RECOVER")
        return [row['data'][0:row['gtrid_length']] for row in resultset]

    def is_disconnect(self, e, connection, cursor):
        if isinstance(e, (self.dbapi.OperationalError, self.dbapi.ProgrammingError)):
            return self._extract_error_code(e) in \
                        (2006, 2013, 2014, 2045, 2055)
        elif isinstance(e, self.dbapi.InterfaceError):
            # if underlying connection is closed,
            # this is the error you get
            return "(0, '')" in str(e)
        else:
            return False

    def _compat_fetchall(self, rp, charset=None):
        """Proxy result rows to smooth over MySQL-Python driver
        inconsistencies."""

        return [_DecodingRowProxy(row, charset) for row in rp.fetchall()]

    def _compat_fetchone(self, rp, charset=None):
        """Proxy a result row to smooth over MySQL-Python driver
        inconsistencies."""

        return _DecodingRowProxy(rp.fetchone(), charset)

    def _compat_first(self, rp, charset=None):
        """Proxy a result row to smooth over MySQL-Python driver
        inconsistencies."""

        return _DecodingRowProxy(rp.first(), charset)

    def _extract_error_code(self, exception):
        raise NotImplementedError()

    def _get_default_schema_name(self, connection):
        return connection.execute('SELECT DATABASE()').scalar()

    def has_table(self, connection, table_name, schema=None):
        # SHOW TABLE STATUS LIKE and SHOW TABLES LIKE do not function properly
        # on macosx (and maybe win?) with multibyte table names.
        #
        # TODO: if this is not a problem on win, make the strategy swappable
        # based on platform.  DESCRIBE is slower.

        # [ticket:726]
        # full_name = self.identifier_preparer.format_table(table,
        #                                                   use_schema=True)

        full_name = '.'.join(self.identifier_preparer._quote_free_identifiers(
            schema, table_name))

        st = "DESCRIBE %s" % full_name
        rs = None
        try:
            try:
                rs = connection.execute(st)
                have = rs.fetchone() is not None
                rs.close()
                return have
            except exc.DBAPIError, e:
                if self._extract_error_code(e.orig) == 1146:
                    return False
                raise
        finally:
            if rs:
                rs.close()

    def initialize(self, connection):
        default.DefaultDialect.initialize(self, connection)
        self._connection_charset = self._detect_charset(connection)
        self._detect_ansiquotes(connection)
        if self._server_ansiquotes:
            # if ansiquotes == True, build a new IdentifierPreparer
            # with the new setting
            self.identifier_preparer = self.preparer(self,
                                server_ansiquotes=self._server_ansiquotes)

    @property
    def _supports_cast(self):
        return self.server_version_info is None or \
                    self.server_version_info >= (4, 0, 2)

    @reflection.cache
    def get_schema_names(self, connection, **kw):
        rp = connection.execute("SHOW schemas")
        return [r[0] for r in rp]

    @reflection.cache
    def get_table_names(self, connection, schema=None, **kw):
        """Return a Unicode SHOW TABLES from a given schema."""
        if schema is not None:
            current_schema = schema
        else:
            current_schema = self.default_schema_name

        charset = self._connection_charset
        if self.server_version_info < (5, 0, 2):
            rp = connection.execute("SHOW TABLES FROM %s" %
                self.identifier_preparer.quote_identifier(current_schema))
            return [row[0] for
                        row in self._compat_fetchall(rp, charset=charset)]
        else:
            rp = connection.execute("SHOW FULL TABLES FROM %s" %
                    self.identifier_preparer.quote_identifier(current_schema))

            return [row[0]
                        for row in self._compat_fetchall(rp, charset=charset)
                                                if row[1] == 'BASE TABLE']

    @reflection.cache
    def get_view_names(self, connection, schema=None, **kw):
        if self.server_version_info < (5, 0, 2):
            raise NotImplementedError
        if schema is None:
            schema = self.default_schema_name
        if self.server_version_info < (5, 0, 2):
            return self.get_table_names(connection, schema)
        charset = self._connection_charset
        rp = connection.execute("SHOW FULL TABLES FROM %s" %
                self.identifier_preparer.quote_identifier(schema))
        return [row[0]
                    for row in self._compat_fetchall(rp, charset=charset)
                                    if row[1] in ('VIEW', 'SYSTEM VIEW')]

    @reflection.cache
    def get_table_options(self, connection, table_name, schema=None, **kw):

        parsed_state = self._parsed_state_or_create(
                                        connection, table_name, schema, **kw)
        return parsed_state.table_options

    @reflection.cache
    def get_columns(self, connection, table_name, schema=None, **kw):
        parsed_state = self._parsed_state_or_create(
                                        connection, table_name, schema, **kw)
        return parsed_state.columns

    @reflection.cache
    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
        parsed_state = self._parsed_state_or_create(
                                        connection, table_name, schema, **kw)
        for key in parsed_state.keys:
            if key['type'] == 'PRIMARY':
                # There can be only one.
                cols = [s[0] for s in key['columns']]
                return {'constrained_columns': cols, 'name': None}
        return {'constrained_columns': [], 'name': None}

    @reflection.cache
    def get_foreign_keys(self, connection, table_name, schema=None, **kw):

        parsed_state = self._parsed_state_or_create(
                                        connection, table_name, schema, **kw)
        default_schema = None

        fkeys = []

        for spec in parsed_state.constraints:
            # only FOREIGN KEYs
            ref_name = spec['table'][-1]
            ref_schema = len(spec['table']) > 1 and spec['table'][-2] or schema

            if not ref_schema:
                if default_schema is None:
                    default_schema = \
                        connection.dialect.default_schema_name
                if schema == default_schema:
                    ref_schema = schema

            loc_names = spec['local']
            ref_names = spec['foreign']

            con_kw = {}
            for opt in ('name', 'onupdate', 'ondelete'):
                if spec.get(opt, False):
                    con_kw[opt] = spec[opt]

            fkey_d = {
                'name': spec['name'],
                'constrained_columns': loc_names,
                'referred_schema': ref_schema,
                'referred_table': ref_name,
                'referred_columns': ref_names,
                'options': con_kw
            }
            fkeys.append(fkey_d)
        return fkeys

    @reflection.cache
    def get_indexes(self, connection, table_name, schema=None, **kw):

        parsed_state = self._parsed_state_or_create(
                                        connection, table_name, schema, **kw)

        indexes = []
        for spec in parsed_state.keys:
            unique = False
            flavor = spec['type']
            if flavor == 'PRIMARY':
                continue
            if flavor == 'UNIQUE':
                unique = True
            elif flavor in (None, 'FULLTEXT', 'SPATIAL'):
                pass
            else:
                self.logger.info(
                    "Converting unknown KEY type %s to a plain KEY" % flavor)
                pass
            index_d = {}
            index_d['name'] = spec['name']
            index_d['column_names'] = [s[0] for s in spec['columns']]
            index_d['unique'] = unique
            index_d['type'] = flavor
            indexes.append(index_d)
        return indexes

    @reflection.cache
    def get_unique_constraints(self, connection, table_name,
                               schema=None, **kw):
        parsed_state = self._parsed_state_or_create(
            connection, table_name, schema, **kw)

        return [
            {
                'name': key['name'],
                'column_names': [col[0] for col in key['columns']]
            }
            for key in parsed_state.keys
            if key['type'] == 'UNIQUE'
        ]

    @reflection.cache
    def get_view_definition(self, connection, view_name, schema=None, **kw):

        charset = self._connection_charset
        full_name = '.'.join(self.identifier_preparer._quote_free_identifiers(
            schema, view_name))
        sql = self._show_create_table(connection, None, charset,
                                      full_name=full_name)
        return sql

    def _parsed_state_or_create(self, connection, table_name,
                                                            schema=None, **kw):
        return self._setup_parser(
                        connection,
                        table_name,
                        schema,
                        info_cache=kw.get('info_cache', None)
                    )

    @util.memoized_property
    def _tabledef_parser(self):
        """return the MySQLTableDefinitionParser, generate if needed.

        The deferred creation ensures that the dialect has
        retrieved server version information first.

        """
        if (self.server_version_info < (4, 1) and self._server_ansiquotes):
            # ANSI_QUOTES doesn't affect SHOW CREATE TABLE on < 4.1
            preparer = self.preparer(self, server_ansiquotes=False)
        else:
            preparer = self.identifier_preparer
        return MySQLTableDefinitionParser(self, preparer)

    @reflection.cache
    def _setup_parser(self, connection, table_name, schema=None, **kw):
        charset = self._connection_charset
        parser = self._tabledef_parser
        full_name = '.'.join(self.identifier_preparer._quote_free_identifiers(
            schema, table_name))
        sql = self._show_create_table(connection, None, charset,
                                      full_name=full_name)
        if sql.startswith('CREATE ALGORITHM'):
            # Adapt views to something table-like.
            columns = self._describe_table(connection, None, charset,
                                           full_name=full_name)
            sql = parser._describe_to_create(table_name, columns)
        return parser.parse(sql, charset)

    def _detect_charset(self, connection):
        raise NotImplementedError()

    def _detect_casing(self, connection):
        """Sniff out identifier case sensitivity.

        Cached per-connection. This value can not change without a server
        restart.

        """
        # http://dev.mysql.com/doc/refman/5.0/en/name-case-sensitivity.html

        charset = self._connection_charset
        row = self._compat_first(connection.execute(
            "SHOW VARIABLES LIKE 'lower_case_table_names'"),
                               charset=charset)
        if not row:
            cs = 0
        else:
            # 4.0.15 returns OFF or ON according to [ticket:489]
            # 3.23 doesn't, 4.0.27 doesn't..
            if row[1] == 'OFF':
                cs = 0
            elif row[1] == 'ON':
                cs = 1
            else:
                cs = int(row[1])
        return cs

    def _detect_collations(self, connection):
        """Pull the active COLLATIONS list from the server.

        Cached per-connection.
        """

        collations = {}
        if self.server_version_info < (4, 1, 0):
            pass
        else:
            charset = self._connection_charset
            rs = connection.execute('SHOW COLLATION')
            for row in self._compat_fetchall(rs, charset):
                collations[row[0]] = row[1]
        return collations

    def _detect_ansiquotes(self, connection):
        """Detect and adjust for the ANSI_QUOTES sql mode."""

        row = self._compat_first(
            connection.execute("SHOW VARIABLES LIKE 'sql_mode'"),
                                charset=self._connection_charset)

        if not row:
            mode = ''
        else:
            mode = row[1] or ''
            # 4.0
            if mode.isdigit():
                mode_no = int(mode)
                mode = (mode_no | 4 == mode_no) and 'ANSI_QUOTES' or ''

        self._server_ansiquotes = 'ANSI_QUOTES' in mode

        # as of MySQL 5.0.1
        self._backslash_escapes = 'NO_BACKSLASH_ESCAPES' not in mode

    def _show_create_table(self, connection, table, charset=None,
                           full_name=None):
        """Run SHOW CREATE TABLE for a ``Table``."""

        if full_name is None:
            full_name = self.identifier_preparer.format_table(table)
        st = "SHOW CREATE TABLE %s" % full_name

        rp = None
        try:
            rp = connection.execute(st)
        except exc.DBAPIError, e:
            if self._extract_error_code(e.orig) == 1146:
                raise exc.NoSuchTableError(full_name)
            else:
                raise
        row = self._compat_first(rp, charset=charset)
        if not row:
            raise exc.NoSuchTableError(full_name)
        return row[1].strip()

        return sql

    def _describe_table(self, connection, table, charset=None,
                             full_name=None):
        """Run DESCRIBE for a ``Table`` and return processed rows."""

        if full_name is None:
            full_name = self.identifier_preparer.format_table(table)
        st = "DESCRIBE %s" % full_name

        rp, rows = None, None
        try:
            try:
                rp = connection.execute(st)
            except exc.DBAPIError, e:
                if self._extract_error_code(e.orig) == 1146:
                    raise exc.NoSuchTableError(full_name)
                else:
                    raise
            rows = self._compat_fetchall(rp, charset=charset)
        finally:
            if rp:
                rp.close()
        return rows


class ReflectedState(object):
    """Stores raw information about a SHOW CREATE TABLE statement."""

    def __init__(self):
        self.columns = []
        self.table_options = {}
        self.table_name = None
        self.keys = []
        self.constraints = []


class MySQLTableDefinitionParser(object):
    """Parses the results of a SHOW CREATE TABLE statement."""

    def __init__(self, dialect, preparer):
        self.dialect = dialect
        self.preparer = preparer
        self._prep_regexes()

    def parse(self, show_create, charset):
        state = ReflectedState()
        state.charset = charset
        for line in re.split(r'\r?\n', show_create):
            if line.startswith('  ' + self.preparer.initial_quote):
                self._parse_column(line, state)
            # a regular table options line
            elif line.startswith(') '):
                self._parse_table_options(line, state)
            # an ANSI-mode table options line
            elif line == ')':
                pass
            elif line.startswith('CREATE '):
                self._parse_table_name(line, state)
            # Not present in real reflection, but may be if
            # loading from a file.
            elif not line:
                pass
            else:
                type_, spec = self._parse_constraints(line)
                if type_ is None:
                    util.warn("Unknown schema content: %r" % line)
                elif type_ == 'key':
                    state.keys.append(spec)
                elif type_ == 'constraint':
                    state.constraints.append(spec)
                else:
                    pass
        return state

    def _parse_constraints(self, line):
        """Parse a KEY or CONSTRAINT line.

        :param line: A line of SHOW CREATE TABLE output
        """

        # KEY
        m = self._re_key.match(line)
        if m:
            spec = m.groupdict()
            # convert columns into name, length pairs
            spec['columns'] = self._parse_keyexprs(spec['columns'])
            return 'key', spec

        # CONSTRAINT
        m = self._re_constraint.match(line)
        if m:
            spec = m.groupdict()
            spec['table'] = \
              self.preparer.unformat_identifiers(spec['table'])
            spec['local'] = [c[0]
                             for c in self._parse_keyexprs(spec['local'])]
            spec['foreign'] = [c[0]
                               for c in self._parse_keyexprs(spec['foreign'])]
            return 'constraint', spec

        # PARTITION and SUBPARTITION
        m = self._re_partition.match(line)
        if m:
            # Punt!
            return 'partition', line

        # No match.
        return (None, line)

    def _parse_table_name(self, line, state):
        """Extract the table name.

        :param line: The first line of SHOW CREATE TABLE
        """

        regex, cleanup = self._pr_name
        m = regex.match(line)
        if m:
            state.table_name = cleanup(m.group('name'))

    def _parse_table_options(self, line, state):
        """Build a dictionary of all reflected table-level options.

        :param line: The final line of SHOW CREATE TABLE output.
        """

        options = {}

        if not line or line == ')':
            pass

        else:
            rest_of_line = line[:]
            for regex, cleanup in self._pr_options:
                m = regex.search(rest_of_line)
                if not m:
                    continue
                directive, value = m.group('directive'), m.group('val')
                if cleanup:
                    value = cleanup(value)
                options[directive.lower()] = value
                rest_of_line = regex.sub('', rest_of_line)

        for nope in ('auto_increment', 'data directory', 'index directory'):
            options.pop(nope, None)

        for opt, val in options.items():
            state.table_options['%s_%s' % (self.dialect.name, opt)] = val

    def _parse_column(self, line, state):
        """Extract column details.

        Falls back to a 'minimal support' variant if full parse fails.

        :param line: Any column-bearing line from SHOW CREATE TABLE
        """

        spec = None
        m = self._re_column.match(line)
        if m:
            spec = m.groupdict()
            spec['full'] = True
        else:
            m = self._re_column_loose.match(line)
            if m:
                spec = m.groupdict()
                spec['full'] = False
        if not spec:
            util.warn("Unknown column definition %r" % line)
            return
        if not spec['full']:
            util.warn("Incomplete reflection of column definition %r" % line)

        name, type_, args, notnull = \
              spec['name'], spec['coltype'], spec['arg'], spec['notnull']

        try:
            col_type = self.dialect.ischema_names[type_]
        except KeyError:
            util.warn("Did not recognize type '%s' of column '%s'" %
                      (type_, name))
            col_type = sqltypes.NullType

        # Column type positional arguments eg. varchar(32)
        if args is None or args == '':
            type_args = []
        elif args[0] == "'" and args[-1] == "'":
            type_args = self._re_csv_str.findall(args)
        else:
            type_args = [int(v) for v in self._re_csv_int.findall(args)]

        # Column type keyword options
        type_kw = {}
        for kw in ('unsigned', 'zerofill'):
            if spec.get(kw, False):
                type_kw[kw] = True
        for kw in ('charset', 'collate'):
            if spec.get(kw, False):
                type_kw[kw] = spec[kw]

        if type_ == 'enum':
            type_args = ENUM._strip_enums(type_args)

        type_instance = col_type(*type_args, **type_kw)

        col_args, col_kw = [], {}

        # NOT NULL
        col_kw['nullable'] = True
        if spec.get('notnull', False):
            col_kw['nullable'] = False

        # AUTO_INCREMENT
        if spec.get('autoincr', False):
            col_kw['autoincrement'] = True
        elif issubclass(col_type, sqltypes.Integer):
            col_kw['autoincrement'] = False

        # DEFAULT
        default = spec.get('default', None)

        if default == 'NULL':
            # eliminates the need to deal with this later.
            default = None

        col_d = dict(name=name, type=type_instance, default=default)
        col_d.update(col_kw)
        state.columns.append(col_d)

    def _describe_to_create(self, table_name, columns):
        """Re-format DESCRIBE output as a SHOW CREATE TABLE string.

        DESCRIBE is a much simpler reflection and is sufficient for
        reflecting views for runtime use.  This method formats DDL
        for columns only- keys are omitted.

        :param columns: A sequence of DESCRIBE or SHOW COLUMNS 6-tuples.
          SHOW FULL COLUMNS FROM rows must be rearranged for use with
          this function.
        """

        buffer = []
        for row in columns:
            (name, col_type, nullable, default, extra) = \
                   [row[i] for i in (0, 1, 2, 4, 5)]

            line = [' ']
            line.append(self.preparer.quote_identifier(name))
            line.append(col_type)
            if not nullable:
                line.append('NOT NULL')
            if default:
                if 'auto_increment' in default:
                    pass
                elif (col_type.startswith('timestamp') and
                      default.startswith('C')):
                    line.append('DEFAULT')
                    line.append(default)
                elif default == 'NULL':
                    line.append('DEFAULT')
                    line.append(default)
                else:
                    line.append('DEFAULT')
                    line.append("'%s'" % default.replace("'", "''"))
            if extra:
                line.append(extra)

            buffer.append(' '.join(line))

        return ''.join([('CREATE TABLE %s (\n' %
                         self.preparer.quote_identifier(table_name)),
                        ',\n'.join(buffer),
                        '\n) '])

    def _parse_keyexprs(self, identifiers):
        """Unpack '"col"(2),"col" ASC'-ish strings into components."""

        return self._re_keyexprs.findall(identifiers)

    def _prep_regexes(self):
        """Pre-compile regular expressions."""

        self._re_columns = []
        self._pr_options = []

        _final = self.preparer.final_quote

        quotes = dict(zip(('iq', 'fq', 'esc_fq'),
                          [re.escape(s) for s in
                           (self.preparer.initial_quote,
                            _final,
                            self.preparer._escape_identifier(_final))]))

        self._pr_name = _pr_compile(
            r'^CREATE (?:\w+ +)?TABLE +'
            r'%(iq)s(?P<name>(?:%(esc_fq)s|[^%(fq)s])+)%(fq)s +\($' % quotes,
            self.preparer._unescape_identifier)

        # `col`,`col2`(32),`col3`(15) DESC
        #
        # Note: ASC and DESC aren't reflected, so we'll punt...
        self._re_keyexprs = _re_compile(
            r'(?:'
            r'(?:%(iq)s((?:%(esc_fq)s|[^%(fq)s])+)%(fq)s)'
            r'(?:\((\d+)\))?(?=\,|$))+' % quotes)

        # 'foo' or 'foo','bar' or 'fo,o','ba''a''r'
        self._re_csv_str = _re_compile(r'\x27(?:\x27\x27|[^\x27])*\x27')

        # 123 or 123,456
        self._re_csv_int = _re_compile(r'\d+')

        # `colname` <type> [type opts]
        #  (NOT NULL | NULL)
        #   DEFAULT ('value' | CURRENT_TIMESTAMP...)
        #   COMMENT 'comment'
        #  COLUMN_FORMAT (FIXED|DYNAMIC|DEFAULT)
        #  STORAGE (DISK|MEMORY)
        self._re_column = _re_compile(
            r'  '
            r'%(iq)s(?P<name>(?:%(esc_fq)s|[^%(fq)s])+)%(fq)s +'
            r'(?P<coltype>\w+)'
            r'(?:\((?P<arg>(?:\d+|\d+,\d+|'
              r'(?:\x27(?:\x27\x27|[^\x27])*\x27,?)+))\))?'
            r'(?: +(?P<unsigned>UNSIGNED))?'
            r'(?: +(?P<zerofill>ZEROFILL))?'
            r'(?: +CHARACTER SET +(?P<charset>[\w_]+))?'
            r'(?: +COLLATE +(?P<collate>[\w_]+))?'
            r'(?: +(?P<notnull>NOT NULL))?'
            r'(?: +DEFAULT +(?P<default>'
              r'(?:NULL|\x27(?:\x27\x27|[^\x27])*\x27|\w+'
              r'(?: +ON UPDATE \w+)?)'
            r'))?'
            r'(?: +(?P<autoincr>AUTO_INCREMENT))?'
            r'(?: +COMMENT +(P<comment>(?:\x27\x27|[^\x27])+))?'
            r'(?: +COLUMN_FORMAT +(?P<colfmt>\w+))?'
            r'(?: +STORAGE +(?P<storage>\w+))?'
            r'(?: +(?P<extra>.*))?'
            r',?$'
            % quotes
            )

        # Fallback, try to parse as little as possible
        self._re_column_loose = _re_compile(
            r'  '
            r'%(iq)s(?P<name>(?:%(esc_fq)s|[^%(fq)s])+)%(fq)s +'
            r'(?P<coltype>\w+)'
            r'(?:\((?P<arg>(?:\d+|\d+,\d+|\x27(?:\x27\x27|[^\x27])+\x27))\))?'
            r'.*?(?P<notnull>NOT NULL)?'
            % quotes
            )

        # (PRIMARY|UNIQUE|FULLTEXT|SPATIAL) INDEX `name` (USING (BTREE|HASH))?
        # (`col` (ASC|DESC)?, `col` (ASC|DESC)?)
        # KEY_BLOCK_SIZE size | WITH PARSER name
        self._re_key = _re_compile(
            r'  '
            r'(?:(?P<type>\S+) )?KEY'
            r'(?: +%(iq)s(?P<name>(?:%(esc_fq)s|[^%(fq)s])+)%(fq)s)?'
            r'(?: +USING +(?P<using_pre>\S+))?'
            r' +\((?P<columns>.+?)\)'
            r'(?: +USING +(?P<using_post>\S+))?'
            r'(?: +KEY_BLOCK_SIZE *[ =]? *(?P<keyblock>\S+))?'
            r'(?: +WITH PARSER +(?P<parser>\S+))?'
            r',?$'
            % quotes
            )

        # CONSTRAINT `name` FOREIGN KEY (`local_col`)
        # REFERENCES `remote` (`remote_col`)
        # MATCH FULL | MATCH PARTIAL | MATCH SIMPLE
        # ON DELETE CASCADE ON UPDATE RESTRICT
        #
        # unique constraints come back as KEYs
        kw = quotes.copy()
        kw['on'] = 'RESTRICT|CASCASDE|SET NULL|NOACTION'
        self._re_constraint = _re_compile(
            r'  '
            r'CONSTRAINT +'
            r'%(iq)s(?P<name>(?:%(esc_fq)s|[^%(fq)s])+)%(fq)s +'
            r'FOREIGN KEY +'
            r'\((?P<local>[^\)]+?)\) REFERENCES +'
            r'(?P<table>%(iq)s[^%(fq)s]+%(fq)s(?:\.%(iq)s[^%(fq)s]+%(fq)s)?) +'
            r'\((?P<foreign>[^\)]+?)\)'
            r'(?: +(?P<match>MATCH \w+))?'
            r'(?: +ON DELETE (?P<ondelete>%(on)s))?'
            r'(?: +ON UPDATE (?P<onupdate>%(on)s))?'
            % kw
            )

        # PARTITION
        #
        # punt!
        self._re_partition = _re_compile(r'(?:.*)(?:SUB)?PARTITION(?:.*)')

        # Table-level options (COLLATE, ENGINE, etc.)
        # Do the string options first, since they have quoted
        # strings we need to get rid of.
        for option in _options_of_type_string:
            self._add_option_string(option)

        for option in ('ENGINE', 'TYPE', 'AUTO_INCREMENT',
                       'AVG_ROW_LENGTH', 'CHARACTER SET',
                       'DEFAULT CHARSET', 'CHECKSUM',
                       'COLLATE', 'DELAY_KEY_WRITE', 'INSERT_METHOD',
                       'MAX_ROWS', 'MIN_ROWS', 'PACK_KEYS', 'ROW_FORMAT',
                       'KEY_BLOCK_SIZE'):
            self._add_option_word(option)

        self._add_option_regex('UNION', r'\([^\)]+\)')
        self._add_option_regex('TABLESPACE', r'.*? STORAGE DISK')
        self._add_option_regex('RAID_TYPE',
          r'\w+\s+RAID_CHUNKS\s*\=\s*\w+RAID_CHUNKSIZE\s*=\s*\w+')

    _optional_equals = r'(?:\s*(?:=\s*)|\s+)'

    def _add_option_string(self, directive):
        regex = (r'(?P<directive>%s)%s'
                 r"'(?P<val>(?:[^']|'')*?)'(?!')" %
                 (re.escape(directive), self._optional_equals))
        self._pr_options.append(_pr_compile(regex, lambda v:
                                v.replace("\\\\", "\\").replace("''", "'")))

    def _add_option_word(self, directive):
        regex = (r'(?P<directive>%s)%s'
                 r'(?P<val>\w+)' %
                 (re.escape(directive), self._optional_equals))
        self._pr_options.append(_pr_compile(regex))

    def _add_option_regex(self, directive, regex):
        regex = (r'(?P<directive>%s)%s'
                 r'(?P<val>%s)' %
                 (re.escape(directive), self._optional_equals, regex))
        self._pr_options.append(_pr_compile(regex))

_options_of_type_string = ('COMMENT', 'DATA DIRECTORY', 'INDEX DIRECTORY',
                           'PASSWORD', 'CONNECTION')

log.class_logger(MySQLTableDefinitionParser)
log.class_logger(MySQLDialect)


class _DecodingRowProxy(object):
    """Return unicode-decoded values based on type inspection.

    Smooth over data type issues (esp. with alpha driver versions) and
    normalize strings as Unicode regardless of user-configured driver
    encoding settings.

    """

    # Some MySQL-python versions can return some columns as
    # sets.Set(['value']) (seriously) but thankfully that doesn't
    # seem to come up in DDL queries.

    def __init__(self, rowproxy, charset):
        self.rowproxy = rowproxy
        self.charset = charset

    def __getitem__(self, index):
        item = self.rowproxy[index]
        if isinstance(item, _array):
            item = item.tostring()
        # Py2K
        if self.charset and isinstance(item, str):
        # end Py2K
        # Py3K
        #if self.charset and isinstance(item, bytes):
            return item.decode(self.charset)
        else:
            return item

    def __getattr__(self, attr):
        item = getattr(self.rowproxy, attr)
        if isinstance(item, _array):
            item = item.tostring()
        # Py2K
        if self.charset and isinstance(item, str):
        # end Py2K
        # Py3K
        #if self.charset and isinstance(item, bytes):
            return item.decode(self.charset)
        else:
            return item


def _pr_compile(regex, cleanup=None):
    """Prepare a 2-tuple of compiled regex and callable."""

    return (_re_compile(regex), cleanup)


def _re_compile(regex):
    """Compile a string to regex, I and UNICODE."""

    return re.compile(regex, re.I | re.UNICODE)
