===============================
Notes about supported databases
===============================

Django attempts to support as many features as possible on all database
backends. However, not all database backends are alike, and we've had to make
design decisions on which features to support and which assumptions we can make
safely.

This file describes some of the features that might be relevant to Django
usage. Of course, it is not intended as a replacement for server-specific
documentation or reference manuals.

MySQL notes
===========

Django expects the database to support transactions, referential integrity,
and Unicode support (UTF-8 encoding). Fortunately, MySQL_ has all these
features as available as far back as 3.23. While it may be possible to use
3.23 or 4.0, you'll probably have less trouble if you use 4.1 or 5.0.

MySQL 4.1
---------

`MySQL 4.1`_ has greatly improved support for character sets. It is possible to
set different default character sets on the database, table, and column.
Previous versions have only a server-wide character set setting. It's also the
first version where the character set can be changed on the fly. 4.1 also has
support for views, but Django currently doesn't use views.

MySQL 5.0
---------

`MySQL 5.0`_ adds the ``information_schema`` database, which contains detailed
data on all database schema. Django's ``inspectdb`` feature uses this
``information_schema`` if it's available. 5.0 also has support for stored
procedures, but Django currently doesn't use stored procedures.

.. _MySQL: http://www.mysql.com/
.. _MySQL 4.1: http://dev.mysql.com/doc/refman/4.1/en/index.html
.. _MySQL 5.0: http://dev.mysql.com/doc/refman/5.0/en/index.html

Storage engines
---------------

MySQL has several `storage engines`_ (previously called table types). You can
change the default storage engine in the server configuration.

The default engine is MyISAM_. The main drawback of MyISAM is that it doesn't
currently support transactions or foreign keys. On the plus side, it's
currently the only engine that supports full-text indexing and searching.

The InnoDB_ engine is fully transactional and supports foreign key references.

The BDB_ engine, like InnoDB, is also fully transactional and supports foreign
key references. However, its use seems to be deprecated.

`Other storage engines`_, including SolidDB_ and Falcon_, are on the horizon.
For now, InnoDB is probably your best choice.

.. _storage engines: http://dev.mysql.com/doc/refman/5.0/en/storage-engines.html
.. _MyISAM: http://dev.mysql.com/doc/refman/5.0/en/myisam-storage-engine.html
.. _BDB: http://dev.mysql.com/doc/refman/5.0/en/bdb-storage-engine.html
.. _InnoDB: http://dev.mysql.com/doc/refman/5.0/en/innodb.html
.. _Other storage engines: http://dev.mysql.com/doc/refman/5.1/en/storage-engines-other.html
.. _SolidDB: http://forge.mysql.com/projects/view.php?id=139
.. _Falcon: http://dev.mysql.com/doc/falcon/en/index.html

MySQLdb
-------

`MySQLdb`_ is the Python interface to MySQL. Version 1.2.1p2 or later is
required for full MySQL support in Django. Earlier versions will not work with
the ``mysql`` backend.

If you are trying to use an older version of MySQL and the ``mysql_old``
backend, then 1.2.0 *might* work for you.

.. _MySQLdb: http://sourceforge.net/projects/mysql-python

Creating your database
----------------------

You can `create your database`_ using the command-line tools and this SQL::

  CREATE DATABASE <dbname> CHARACTER SET utf8;

This ensures all tables and columns will use UTF-8 by default.

.. _create your database: http://dev.mysql.com/doc/refman/5.0/en/create-database.html

Connecting to the database
--------------------------

Refer to the `settings documentation`_.

Connection settings are used in this order:

 1. ``DATABASE_OPTIONS``
 2. ``DATABASE_NAME``, ``DATABASE_USER``, ``DATABASE_PASSWORD``, ``DATABASE_HOST``,
    ``DATABASE_PORT``
 3. MySQL option files.

In other words, if you set the name of the database in ``DATABASE_OPTIONS``,
this will take precedence over ``DATABASE_NAME``, which would override
anything in a `MySQL option file`_.

Here's a sample configuration which uses a MySQL option file::

  # settings.py
  DATABASE_ENGINE = "mysql"
  DATABASE_OPTIONS = {
      'read_default_file': '/path/to/my.cnf',
      }

  # my.cnf
  [client]
  database = DATABASE_NAME
  user = DATABASE_USER
  passwd = DATABASE_PASSWORD
  default-character-set = utf8

Several other MySQLdb connection options may be useful, such as ``ssl``,
``use_unicode``, ``init_command``, and ``sql_mode``. Consult the
`MySQLdb documentation`_ for more details.

.. _settings documentation: http://www.djangoproject.com/documentation/settings/#database-engine
.. _MySQL option file: http://dev.mysql.com/doc/refman/5.0/en/option-files.html
.. _MySQLdb documentation: http://mysql-python.sourceforge.net/

Creating your tables
--------------------

When Django generates the schema, it doesn't specify a storage engine, so
tables will be created with whatever default storage engine your database
server is configured for. The easiest solution is to set your database server's
default storage engine to the desired engine.

If you're using a hosting service and can't change your server's default
storage engine, you have a couple of options.

    * After the tables are created, execute an ``ALTER TABLE`` statement to
      convert a table to a new storage engine (such as InnoDB)::

          ALTER TABLE <tablename> ENGINE=INNODB;

      This can be tedious if you have a lot of tables.

    * Another option is to use the ``init_command`` option for MySQLdb prior to
      creating your tables::

          DATABASE_OPTIONS = {
              # ...
             "init_command": "SET storage_engine=INNODB",
              # ...
          }

      This sets the default storage engine upon connecting to the database.
      After your tables have been created, you should remove this option.

    * Another method for changing the storage engine is described in
      AlterModelOnSyncDB_.

.. _AlterModelOnSyncDB: http://code.djangoproject.com/wiki/AlterModelOnSyncDB

