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Module « sqlalchemy »

Fonction nulls_first - module sqlalchemy

Signature de la fonction nulls_first

def nulls_first(column: '_ColumnExpressionArgument[_T]') -> 'UnaryExpression[_T]' 

Description

help(sqlalchemy.nulls_first)

Produce the ``NULLS FIRST`` modifier for an ``ORDER BY`` expression.

:func:`.nulls_first` is intended to modify the expression produced
by :func:`.asc` or :func:`.desc`, and indicates how NULL values
should be handled when they are encountered during ordering::


    from sqlalchemy import desc, nulls_first

    stmt = select(users_table).order_by(nulls_first(desc(users_table.c.name)))

The SQL expression from the above would resemble:

.. sourcecode:: sql

    SELECT id, name FROM user ORDER BY name DESC NULLS FIRST

Like :func:`.asc` and :func:`.desc`, :func:`.nulls_first` is typically
invoked from the column expression itself using
:meth:`_expression.ColumnElement.nulls_first`,
rather than as its standalone
function version, as in::

    stmt = select(users_table).order_by(
        users_table.c.name.desc().nulls_first()
    )

.. versionchanged:: 1.4 :func:`.nulls_first` is renamed from
    :func:`.nullsfirst` in previous releases.
    The previous name remains available for backwards compatibility.

.. seealso::

    :func:`.asc`

    :func:`.desc`

    :func:`.nulls_last`

    :meth:`_expression.Select.order_by`

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