.. _topics-db-sql:

Performing raw SQL queries
==========================

Feel free to write custom SQL statements in custom model methods and
module-level methods. The object ``django.db.connection`` represents the
current database connection, and ``django.db.transaction`` represents the
current database transaction. To use the database connection, call
``connection.cursor()`` to get a cursor object. Then, call
``cursor.execute(sql, [params])`` to execute the SQL and ``cursor.fetchone()``
or ``cursor.fetchall()`` to return the resulting rows. After performing a data
changing operation, you should then call
``transaction.commit_unless_managed()`` to ensure your changes are committed
to the database. If your query is purely a data retrieval operation, no commit
is required. For example::

    def my_custom_sql(self):
        from django.db import connection, transaction
        cursor = connection.cursor()

        # Data modifying operation - commit required
        cursor.execute("UPDATE bar SET foo = 1 WHERE baz = %s", [self.baz])
        transaction.commit_unless_managed()

        # Data retrieval operation - no commit required
        cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
        row = cursor.fetchone()

        return row

``connection`` and ``cursor`` mostly implement the standard `Python DB-API`_
(except when it comes to :ref:`transaction handling <topics-db-transactions>`).
If you're not familiar with the Python DB-API, note that the SQL statement in
``cursor.execute()`` uses placeholders, ``"%s"``, rather than adding parameters
directly within the SQL. If you use this technique, the underlying database
library will automatically add quotes and escaping to your parameter(s) as
necessary. (Also note that Django expects the ``"%s"`` placeholder, *not* the
``"?"`` placeholder, which is used by the SQLite Python bindings. This is for
the sake of consistency and sanity.)

A final note: If all you want to do is a custom ``WHERE`` clause, you can just
use the ``where``, ``tables`` and ``params`` arguments to the standard lookup
API.

.. _Python DB-API: http://www.python.org/peps/pep-0249.html

