Minor edits to docs/topics/db/queries.txt.

:class:`~django.db.models.Manager` on your model class.

A :class:`~django.db.models.query.QuerySet` represents a collection of objects

from your database. It can have zero, one or many *filters* -- criteria that

narrow down the collection based on given parameters. In SQL terms, a

from your database. It can have zero, one or many *filters*. Filters narrow

down the query results based on the given parameters. In SQL terms, a

:class:`~django.db.models.query.QuerySet` equates to a ``SELECT`` statement,

and a filter is a limiting clause such as ``WHERE`` or ``LIMIT``.

These three ``QuerySets`` are separate. The first is a base

:class:`~django.db.models.query.QuerySet` containing all entries that contain a

headline starting with "What". The second is a subset of the first, with an

additional criteria that excludes records whose ``pub_date`` is greater than

now. The third is a subset of the first, with an additional criteria that

selects only the records whose ``pub_date`` is greater than now. The initial

:class:`~django.db.models.query.QuerySet` (``q1``) is unaffected by the

additional criteria that excludes records whose ``pub_date`` is today or in the

future. The third is a subset of the first, with an additional criteria that

selects only the records whose ``pub_date`` is today or in the future. The

initial :class:`~django.db.models.query.QuerySet` (``q1``) is unaffected by the

refinement process.

.. _querysets-are-lazy:

    >>> e.blog = some_blog

    >>> e.save()

If a :class:`~django.db.models.ForeignKey` field has ``null=True`` set (i.e., it allows ``NULL``

values), you can assign ``None`` to it. Example::

If a :class:`~django.db.models.ForeignKey` field has ``null=True`` set (i.e.,

it allows ``NULL`` values), you can assign ``None`` to remove the relation.

Example::

    >>> e = Entry.objects.get(id=2)

    >>> e.blog = None