text: """
  MySQL database backend for Django.
  
  Requires MySQLdb: http://sourceforge.net/projects/mysql-python
  """
  from __future__ import unicode_literals
  
  import datetime
  import re
  import sys
  import warnings
  
  try:
      import MySQLdb as Database
  except ImportError as e:
      from django.core.exceptions import ImproperlyConfigured
      raise ImproperlyConfigured("Error loading MySQLdb module: %s" % e)
  
  from django.utils.functional import cached_property
  
  # We want version (1, 2, 1, 'final', 2) or later. We can't just use
  # lexicographic ordering in this check because then (1, 2, 1, 'gamma')
  # inadvertently passes the version test.
  version = Database.version_info
  if (version < (1, 2, 1) or (version[:3] == (1, 2, 1) and
          (len(version) < 5 or version[3] != 'final' or version[4] < 2))):
      from django.core.exceptions import ImproperlyConfigured
      raise ImproperlyConfigured("MySQLdb-1.2.1p2 or newer is required; you have %s" % Database.__version__)
  
  from MySQLdb.converters import conversions, Thing2Literal
  from MySQLdb.constants import FIELD_TYPE, CLIENT
  
  from django.db import utils
  from django.db.backends import *
  from django.db.backends.signals import connection_created
  from django.db.backends.mysql.client import DatabaseClient
  from django.db.backends.mysql.creation import DatabaseCreation
  from django.db.backends.mysql.introspection import DatabaseIntrospection
  from django.db.backends.mysql.validation import DatabaseValidation
  from django.utils.encoding import force_str
  from django.utils.functional import cached_property
  from django.utils.safestring import SafeBytes, SafeText
  from django.utils import six
  from django.utils import timezone
  
  # Raise exceptions for database warnings if DEBUG is on
  from django.conf import settings
  if settings.DEBUG:
      warnings.filterwarnings("error", category=Database.Warning)
  
  DatabaseError = Database.DatabaseError
  IntegrityError = Database.IntegrityError
  
  # It's impossible to import datetime_or_None directly from MySQLdb.times
  parse_datetime = conversions[FIELD_TYPE.DATETIME]
  
  def parse_datetime_with_timezone_support(value):
      dt = parse_datetime(value)
      # Confirm that dt is naive before overwriting its tzinfo.
      if dt is not None and settings.USE_TZ and timezone.is_naive(dt):
          dt = dt.replace(tzinfo=timezone.utc)
      return dt
  
  def adapt_datetime_with_timezone_support(value, conv):
      # Equivalent to DateTimeField.get_db_prep_value. Used only by raw SQL.
      if settings.USE_TZ:
          if timezone.is_naive(value):
              warnings.warn("SQLite received a naive datetime (%s)"
                            " while time zone support is active." % value,
                            RuntimeWarning)
              default_timezone = timezone.get_default_timezone()
              value = timezone.make_aware(value, default_timezone)
          value = value.astimezone(timezone.utc).replace(tzinfo=None)
      return Thing2Literal(value.strftime("%Y-%m-%d %H:%M:%S"), conv)
  
  # MySQLdb-1.2.1 returns TIME columns as timedelta -- they are more like
  # timedelta in terms of actual behavior as they are signed and include days --
  # and Django expects time, so we still need to override that. We also need to
  # add special handling for SafeText and SafeBytes as MySQLdb's type
  # checking is too tight to catch those (see Django ticket #6052).
  # Finally, MySQLdb always returns naive datetime objects. However, when
  # timezone support is active, Django expects timezone-aware datetime objects.
  django_conversions = conversions.copy()
  django_conversions.update({
      FIELD_TYPE.TIME: util.typecast_time,
      FIELD_TYPE.DECIMAL: util.typecast_decimal,
      FIELD_TYPE.NEWDECIMAL: util.typecast_decimal,
      FIELD_TYPE.DATETIME: parse_datetime_with_timezone_support,
      datetime.datetime: adapt_datetime_with_timezone_support,
  })
  
  # This should match the numerical portion of the version numbers (we can treat
  # versions like 5.0.24 and 5.0.24a as the same). Based on the list of version
  # at http://dev.mysql.com/doc/refman/4.1/en/news.html and
  # http://dev.mysql.com/doc/refman/5.0/en/news.html .
  server_version_re = re.compile(r'(\d{1,2})\.(\d{1,2})\.(\d{1,2})')
  
  # MySQLdb-1.2.1 and newer automatically makes use of SHOW WARNINGS on
  # MySQL-4.1 and newer, so the MysqlDebugWrapper is unnecessary. Since the
  # point is to raise Warnings as exceptions, this can be done with the Python
  # warning module, and this is setup when the connection is created, and the
  # standard util.CursorDebugWrapper can be used. Also, using sql_mode
  # TRADITIONAL will automatically cause most warnings to be treated as errors.
  
  class CursorWrapper(object):
      """
      A thin wrapper around MySQLdb's normal cursor class so that we can catch
      particular exception instances and reraise them with the right types.
  
      Implemented as a wrapper, rather than a subclass, so that we aren't stuck
      to the particular underlying representation returned by Connection.cursor().
      """
      codes_for_integrityerror = (1048,)
  
      def __init__(self, cursor):
          self.cursor = cursor
  
      def execute(self, query, args=None):
          try:
              return self.cursor.execute(query, args)
          except Database.IntegrityError as e:
              six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
          except Database.OperationalError as e:
              # Map some error codes to IntegrityError, since they seem to be
              # misclassified and Django would prefer the more logical place.
              if e[0] in self.codes_for_integrityerror:
                  six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
              six.reraise(utils.DatabaseError, utils.DatabaseError(*tuple(e.args)), sys.exc_info()[2])
          except Database.DatabaseError as e:
              six.reraise(utils.DatabaseError, utils.DatabaseError(*tuple(e.args)), sys.exc_info()[2])
  
      def executemany(self, query, args):
          try:
              return self.cursor.executemany(query, args)
          except Database.IntegrityError as e:
              six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
          except Database.OperationalError as e:
              # Map some error codes to IntegrityError, since they seem to be
              # misclassified and Django would prefer the more logical place.
              if e[0] in self.codes_for_integrityerror:
                  six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
              six.reraise(utils.DatabaseError, utils.DatabaseError(*tuple(e.args)), sys.exc_info()[2])
          except Database.DatabaseError as e:
              six.reraise(utils.DatabaseError, utils.DatabaseError(*tuple(e.args)), sys.exc_info()[2])
  
      def __getattr__(self, attr):
          if attr in self.__dict__:
              return self.__dict__[attr]
          else:
              return getattr(self.cursor, attr)
  
      def __iter__(self):
          return iter(self.cursor)
  
  class DatabaseFeatures(BaseDatabaseFeatures):
      empty_fetchmany_value = ()
      update_can_self_select = False
      allows_group_by_pk = True
      related_fields_match_type = True
      allow_sliced_subqueries = False
      has_bulk_insert = True
      has_select_for_update = True
      has_select_for_update_nowait = False
      supports_forward_references = False
      supports_long_model_names = False
      supports_microsecond_precision = False
      supports_regex_backreferencing = False
      supports_date_lookup_using_string = False
      supports_timezones = False
      requires_explicit_null_ordering_when_grouping = True
      allows_primary_key_0 = False
      uses_savepoints = True
  
      def __init__(self, connection):
          super(DatabaseFeatures, self).__init__(connection)
  
      @cached_property
      def _mysql_storage_engine(self):
          "Internal method used in Django tests. Don't rely on this from your code"
          cursor = self.connection.cursor()
          cursor.execute('CREATE TABLE INTROSPECT_TEST (X INT)')
          # This command is MySQL specific; the second column
          # will tell you the default table type of the created
          # table. Since all Django's test tables will have the same
          # table type, that's enough to evaluate the feature.
          cursor.execute("SHOW TABLE STATUS WHERE Name='INTROSPECT_TEST'")
          result = cursor.fetchone()
          cursor.execute('DROP TABLE INTROSPECT_TEST')
          return result[1]
  
      @cached_property
      def can_introspect_foreign_keys(self):
          "Confirm support for introspected foreign keys"
          return self._mysql_storage_engine != 'MyISAM'
  
  class DatabaseOperations(BaseDatabaseOperations):
      compiler_module = "django.db.backends.mysql.compiler"
  
      def date_extract_sql(self, lookup_type, field_name):
          # http://dev.mysql.com/doc/mysql/en/date-and-time-functions.html
          if lookup_type == 'week_day':
              # DAYOFWEEK() returns an integer, 1-7, Sunday=1.
              # Note: WEEKDAY() returns 0-6, Monday=0.
              return "DAYOFWEEK(%s)" % field_name
          else:
              return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)
  
      def date_trunc_sql(self, lookup_type, field_name):
          fields = ['year', 'month', 'day', 'hour', 'minute', 'second']
          format = ('%%Y-', '%%m', '-%%d', ' %%H:', '%%i', ':%%s') # Use double percents to escape.
          format_def = ('0000-', '01', '-01', ' 00:', '00', ':00')
          try:
              i = fields.index(lookup_type) + 1
          except ValueError:
              sql = field_name
          else:
              format_str = ''.join([f for f in format[:i]] + [f for f in format_def[i:]])
              sql = "CAST(DATE_FORMAT(%s, '%s') AS DATETIME)" % (field_name, format_str)
          return sql
  
      def date_interval_sql(self, sql, connector, timedelta):
          return "(%s %s INTERVAL '%d 0:0:%d:%d' DAY_MICROSECOND)" % (sql, connector,
                  timedelta.days, timedelta.seconds, timedelta.microseconds)
  
      def drop_foreignkey_sql(self):
          return "DROP FOREIGN KEY"
  
      def force_no_ordering(self):
          """
          "ORDER BY NULL" prevents MySQL from implicitly ordering by grouped
          columns. If no ordering would otherwise be applied, we don't want any
          implicit sorting going on.
          """
          return ["NULL"]
  
      def fulltext_search_sql(self, field_name):
          return 'MATCH (%s) AGAINST (%%s IN BOOLEAN MODE)' % field_name
  
      def last_executed_query(self, cursor, sql, params):
          # With MySQLdb, cursor objects have an (undocumented) "_last_executed"
          # attribute where the exact query sent to the database is saved.
          # See MySQLdb/cursors.py in the source distribution.
          return cursor._last_executed.decode('utf-8')
  
      def no_limit_value(self):
          # 2**64 - 1, as recommended by the MySQL documentation
          return 18446744073709551615
  
      def quote_name(self, name):
          if name.startswith("`") and name.endswith("`"):
              return name # Quoting once is enough.
          return "`%s`" % name
  
      def random_function_sql(self):
          return 'RAND()'
  
      def sql_flush(self, style, tables, sequences):
          # NB: The generated SQL below is specific to MySQL
          # 'TRUNCATE x;', 'TRUNCATE y;', 'TRUNCATE z;'... style SQL statements
          # to clear all tables of all data
          if tables:
              sql = ['SET FOREIGN_KEY_CHECKS = 0;']
              for table in tables:
                  sql.append('%s %s;' % (style.SQL_KEYWORD('TRUNCATE'), style.SQL_FIELD(self.quote_name(table))))
              sql.append('SET FOREIGN_KEY_CHECKS = 1;')
              sql.extend(self.sequence_reset_by_name_sql(style, sequences))
              return sql
          else:
              return []
  
      def sequence_reset_by_name_sql(self, style, sequences):
          # Truncate already resets the AUTO_INCREMENT field from
          # MySQL version 5.0.13 onwards. Refs #16961.
          if self.connection.mysql_version < (5, 0, 13):
              return ["%s %s %s %s %s;" % \
                      (style.SQL_KEYWORD('ALTER'),
                      style.SQL_KEYWORD('TABLE'),
                      style.SQL_TABLE(self.quote_name(sequence['table'])),
                      style.SQL_KEYWORD('AUTO_INCREMENT'),
                      style.SQL_FIELD('= 1'),
                      ) for sequence in sequences]
          else:
              return []
  
      def validate_autopk_value(self, value):
          # MySQLism: zero in AUTO_INCREMENT field does not work. Refs #17653.
          if value == 0:
              raise ValueError('The database backend does not accept 0 as a '
                               'value for AutoField.')
          return value
  
      def value_to_db_datetime(self, value):
          if value is None:
              return None
  
          # MySQL doesn't support tz-aware datetimes
          if timezone.is_aware(value):
              if settings.USE_TZ:
                  value = value.astimezone(timezone.utc).replace(tzinfo=None)
              else:
                  raise ValueError("MySQL backend does not support timezone-aware datetimes when USE_TZ is False.")
  
          # MySQL doesn't support microseconds
          return six.text_type(value.replace(microsecond=0))
  
      def value_to_db_time(self, value):
          if value is None:
              return None
  
          # MySQL doesn't support tz-aware times
          if timezone.is_aware(value):
              raise ValueError("MySQL backend does not support timezone-aware times.")
  
          # MySQL doesn't support microseconds
          return six.text_type(value.replace(microsecond=0))
  
      def year_lookup_bounds(self, value):
          # Again, no microseconds
          first = '%s-01-01 00:00:00'
          second = '%s-12-31 23:59:59.99'
          return [first % value, second % value]
  
      def max_name_length(self):
          return 64
  
      def bulk_insert_sql(self, fields, num_values):
          items_sql = "(%s)" % ", ".join(["%s"] * len(fields))
          return "VALUES " + ", ".join([items_sql] * num_values)
  
      def savepoint_create_sql(self, sid):
          return "SAVEPOINT %s" % sid
  
      def savepoint_commit_sql(self, sid):
          return "RELEASE SAVEPOINT %s" % sid
  
      def savepoint_rollback_sql(self, sid):
          return "ROLLBACK TO SAVEPOINT %s" % sid
  
  class DatabaseWrapper(BaseDatabaseWrapper):
      vendor = 'mysql'
      operators = {
          'exact': '= %s',
          'iexact': 'LIKE %s',
          'contains': 'LIKE BINARY %s',
          'icontains': 'LIKE %s',
          'regex': 'REGEXP BINARY %s',
          'iregex': 'REGEXP %s',
          'gt': '> %s',
          'gte': '>= %s',
          'lt': '< %s',
          'lte': '<= %s',
          'startswith': 'LIKE BINARY %s',
          'endswith': 'LIKE BINARY %s',
          'istartswith': 'LIKE %s',
          'iendswith': 'LIKE %s',
      }
  
      def __init__(self, *args, **kwargs):
          super(DatabaseWrapper, self).__init__(*args, **kwargs)
  
          self.server_version = None
          self.features = DatabaseFeatures(self)
          self.ops = DatabaseOperations(self)
          self.client = DatabaseClient(self)
          self.creation = DatabaseCreation(self)
          self.introspection = DatabaseIntrospection(self)
          self.validation = DatabaseValidation(self)
  
      def _valid_connection(self):
          if self.connection is not None:
              try:
                  self.connection.ping()
                  return True
              except DatabaseError:
                  self.connection.close()
                  self.connection = None
          return False
  
      def _cursor(self):
          new_connection = False
          if not self._valid_connection():
              new_connection = True
              kwargs = {
                  'conv': django_conversions,
                  'charset': 'utf8',
                  'use_unicode': True,
              }
              settings_dict = self.settings_dict
              if settings_dict['USER']:
                  kwargs['user'] = settings_dict['USER']
              if settings_dict['NAME']:
                  kwargs['db'] = settings_dict['NAME']
              if settings_dict['PASSWORD']:
                  kwargs['passwd'] = force_str(settings_dict['PASSWORD'])
              if settings_dict['HOST'].startswith('/'):
                  kwargs['unix_socket'] = settings_dict['HOST']
              elif settings_dict['HOST']:
                  kwargs['host'] = settings_dict['HOST']
              if settings_dict['PORT']:
                  kwargs['port'] = int(settings_dict['PORT'])
              # We need the number of potentially affected rows after an
              # "UPDATE", not the number of changed rows.
              kwargs['client_flag'] = CLIENT.FOUND_ROWS
              kwargs.update(settings_dict['OPTIONS'])
              self.connection = Database.connect(**kwargs)
              self.connection.encoders[SafeText] = self.connection.encoders[six.text_type]
              self.connection.encoders[SafeBytes] = self.connection.encoders[bytes]
              connection_created.send(sender=self.__class__, connection=self)
          cursor = self.connection.cursor()
          if new_connection:
              # SQL_AUTO_IS_NULL in MySQL controls whether an AUTO_INCREMENT column
              # on a recently-inserted row will return when the field is tested for
              # NULL.  Disabling this value brings this aspect of MySQL in line with
              # SQL standards.
              cursor.execute('SET SQL_AUTO_IS_NULL = 0')
          return CursorWrapper(cursor)
  
      def _rollback(self):
          try:
              BaseDatabaseWrapper._rollback(self)
          except Database.NotSupportedError:
              pass
  
      @cached_property
      def mysql_version(self):
          if not self.server_version:
              new_connection = False
              if not self._valid_connection():
                  # Ensure we have a connection with the DB by using a temporary
                  # cursor
                  new_connection = True
                  self.cursor().close()
              server_info = self.connection.get_server_info()
              if new_connection:
                  # Make sure we close the connection
                  self.connection.close()
                  self.connection = None
              m = server_version_re.match(server_info)
              if not m:
                  raise Exception('Unable to determine MySQL version from version string %r' % server_info)
              self.server_version = tuple([int(x) for x in m.groups()])
          return self.server_version
  
      def disable_constraint_checking(self):
          """
          Disables foreign key checks, primarily for use in adding rows with forward references. Always returns True,
          to indicate constraint checks need to be re-enabled.
          """
          self.cursor().execute('SET foreign_key_checks=0')
          return True
  
      def enable_constraint_checking(self):
          """
          Re-enable foreign key checks after they have been disabled.
          """
          self.cursor().execute('SET foreign_key_checks=1')
  
      def check_constraints(self, table_names=None):
          """
          Checks each table name in `table_names` for rows with invalid foreign key references. This method is
          intended to be used in conjunction with `disable_constraint_checking()` and `enable_constraint_checking()`, to
          determine if rows with invalid references were entered while constraint checks were off.
  
          Raises an IntegrityError on the first invalid foreign key reference encountered (if any) and provides
          detailed information about the invalid reference in the error message.
  
          Backends can override this method if they can more directly apply constraint checking (e.g. via "SET CONSTRAINTS
          ALL IMMEDIATE")
          """
          cursor = self.cursor()
          if table_names is None:
              table_names = self.introspection.table_names(cursor)
          for table_name in table_names:
              primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
              if not primary_key_column_name:
                  continue
              key_columns = self.introspection.get_key_columns(cursor, table_name)
              for column_name, referenced_table_name, referenced_column_name in key_columns:
                  cursor.execute("""
                      SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
                      LEFT JOIN `%s` as REFERRED
                      ON (REFERRING.`%s` = REFERRED.`%s`)
                      WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL"""
                      % (primary_key_column_name, column_name, table_name, referenced_table_name,
                      column_name, referenced_column_name, column_name, referenced_column_name))
                  for bad_row in cursor.fetchall():
                      raise utils.IntegrityError("The row in table '%s' with primary key '%s' has an invalid "
                          "foreign key: %s.%s contains a value '%s' that does not have a corresponding value in %s.%s."
                          % (table_name, bad_row[0],
                          table_name, column_name, bad_row[1],
                          referenced_table_name, referenced_column_name))
  