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FAQ: Databases and models

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.. _faq-see-raw-sql-queries:

How can I see the raw SQL queries Django is running?

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Make sure your Django :setting:`DEBUG` setting is set to ``True``.

Then do this::

    >>> from django.db import connection

    >>> connection.queries

    [{'sql': 'SELECT polls_polls.id, polls_polls.question, polls_polls.pub_date FROM polls_polls',

    'time': '0.002'}]

``connection.queries`` is only available if :setting:`DEBUG` is ``True``.

It's a list of dictionaries in order of query execution. Each dictionary has

the following::

    ``sql`` -- The raw SQL statement

    ``time`` -- How long the statement took to execute, in seconds.

``connection.queries`` includes all SQL statements -- INSERTs, UPDATES,

SELECTs, etc. Each time your app hits the database, the query will be recorded.

If you are using :doc:`multiple databases</topics/db/multi-db>`, you can use the

same interface on each member of the ``connections`` dictionary::

    >>> from django.db import connections

    >>> connections['my_db_alias'].queries

If you need to clear the query list manually at any point in your functions,

call ``reset_queries()``, like this::

    from django.db import reset_queries

    reset_queries()

Can I use Django with a preexisting database?

=============================================

Yes. See :doc:`Integrating with a legacy database </howto/legacy-databases>`.

If I make changes to a model, how do I update the database?

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Take a look at Django's support for :mod:`schema migrations

<django.db.migrations>`.

If you don't mind clearing data, your project's ``manage.py`` utility has a

:djadmin:`flush` option to reset the database to the state it was in

immediately after :djadmin:`migrate` was executed.

Do Django models support multiple-column primary keys?

======================================================

No. Only single-column primary keys are supported.

But this isn't an issue in practice, because there's nothing stopping you from

adding other constraints (using the ``unique_together`` model option or

creating the constraint directly in your database), and enforcing the

uniqueness at that level. Single-column primary keys are needed for things such

as the admin interface to work; e.g., you need a single value to specify

an object to edit or delete.

Does Django support NoSQL databases?

====================================

NoSQL databases are not officially supported by Django itself. There are,

however, a number of side projects and forks which allow NoSQL functionality in

Django.

You can take a look on `the wiki page`_ which discusses some projects.

.. _the wiki page: https://code.djangoproject.com/wiki/NoSqlSupport

How do I add database-specific options to my CREATE TABLE statements, such as specifying MyISAM as the table type?

==================================================================================================================

We try to avoid adding special cases in the Django code to accommodate all the

database-specific options such as table type, etc. If you'd like to use any of

these options, create a migration with a

:class:`~django.db.migrations.operations.RunSQL` operation that contains

``ALTER TABLE`` statements that do what you want to do.

For example, if you're using MySQL and want your tables to use the MyISAM table

type, use the following SQL::

    ALTER TABLE myapp_mytable ENGINE=MyISAM;