title: how Update column data type in Django
body: <p>I have new to python and django I am creating poll application and in that application after creating models poll and choice using "South". I want to changer the length of question field from 200 to 300 but I am not able to achieve it even using south as well.</p>
  
  <p>I have run python manage.py schemamigration polls --initial command to create migration file then I make change in poll question field that is (question = models.CharField(max_length=250)) change max_length from 200 to 250.</p>
  
  <p>and the again run  python manage.py schemamigration polls --auto this will generate new migration file.</p>
  
  <p>after that all stuff I run python manage.py migrate polls and it shows following error :</p>
  
  <pre><code>C:\Python26\lib\site-packages\MySQLdb\__init__.py:34: DeprecationWarning: the sets module is deprecated
    from sets import ImmutableSet
  Running migrations for polls:
   - Migrating forwards to 0003_auto__chg_field_poll_question.
   &gt; polls:0003_auto__chg_field_poll_question
   ! Error found during real run of migration! Aborting.
  
   ! Since you have a database that does not support running
   ! schema-altering statements in transactions, we have had
   ! to leave it in an interim state between migrations.
  
  ! You *might* be able to recover with:   = ALTER TABLE `polls_poll` ; []
     = ALTER TABLE `polls_poll` MODIFY `question` varchar(200) NOT NULL;; []
     = ALTER TABLE `polls_poll` ALTER COLUMN `question` DROP DEFAULT; []
  
   ! The South developers regret this has happened, and would
   ! like to gently persuade you to consider a slightly
   ! easier-to-deal-with DBMS.
   ! NOTE: The error which caused the migration to fail is further up.
  Traceback (most recent call last):
    File "manage.py", line 11, in &lt;module&gt;
      execute_manager(settings)
    File "C:\Python26\lib\site-packages\django\core\management\__init__.py", line
  362, in execute_manager
      utility.execute()
    File "C:\Python26\lib\site-packages\django\core\management\__init__.py", line
  303, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "C:\Python26\lib\site-packages\django\core\management\base.py", line 195,
   in run_from_argv
      self.execute(*args, **options.__dict__)
    File "C:\Python26\lib\site-packages\django\core\management\base.py", line 222,
   in execute
      output = self.handle(*args, **options)
    File "C:\Python26\lib\site-packages\south\management\commands\migrate.py", lin
  e 109, in handle
      ignore_ghosts = ignore_ghosts,
    File "C:\Python26\lib\site-packages\south\migration\__init__.py", line 202, in
   migrate_app
      success = migrator.migrate_many(target, workplan, database)
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 220, i
  n migrate_many
      result = migrator.__class__.migrate_many(migrator, target, migrations, datab
  ase)
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 291, i
  n migrate_many
      result = self.migrate(migration, database)
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 125, i
  n migrate
      result = self.run(migration)
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 99, in
   run
      return self.run_migration(migration)
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 81, in
   run_migration
      migration_function()
    File "C:\Python26\lib\site-packages\south\migration\migrators.py", line 57, in
   &lt;lambda&gt;
      return (lambda: direction(orm))
    File "C:\mysite\..\mysite\polls\migrations\0003_auto__chg_field_poll_question.
  py", line 12, in forwards
      db.alter_column('polls_poll', 'question', self.gf('django.db.models.fields.C
  harField')(max_length=250))
    File "C:\Python26\lib\site-packages\south\db\generic.py", line 330, in alter_c
  olumn
      self.delete_foreign_key(table_name, name)
    File "C:\Python26\lib\site-packages\south\db\generic.py", line 588, in delete_
  foreign_key
      constraints = list(self._constraints_affecting_columns(table_name, [column],
   "FOREIGN KEY"))
    File "C:\Python26\lib\site-packages\south\db\mysql.py", line 140, in _constrai
  nts_affecting_columns
      """, [db_name, table_name, type])
    File "C:\Python26\lib\site-packages\south\db\generic.py", line 134, in execute
  
      cursor.execute(sql, params)
    File "C:\Python26\lib\site-packages\django\db\backends\util.py", line 19, in e
  xecute
      return self.cursor.execute(sql, params)
    File "C:\Python26\lib\site-packages\django\db\backends\mysql\base.py", line 84
  , in execute
      return self.cursor.execute(query, args)
    File "C:\Python26\lib\site-packages\MySQLdb\cursors.py", line 168, in execute
      if not self._defer_warnings: self._warning_check()
    File "C:\Python26\lib\site-packages\MySQLdb\cursors.py", line 82, in _warning_
  check
      warn(w[-1], self.Warning, 3)
  _mysql_exceptions.Warning: Can't find file: 'slow_log' (errno: 2)
  </code></pre>
  
  <p>Please help me </p>
  
  <p>0003 Look like : </p>
  
  <p>class Migration(SchemaMigration):</p>
  
  <pre><code>def forwards(self, orm):
  
      # Changing field 'Poll.question'
      db.alter_column('polls_poll', 'question', self.gf('django.db.models.fields.CharField')(max_length=250))
  
  
  def backwards(self, orm):
  
      # Changing field 'Poll.question'
      db.alter_column('polls_poll', 'question', self.gf('django.db.models.fields.CharField')(max_length=200))
  </code></pre>
  
  <p>Ansh J</p>