Module « sqlalchemy »

Fonction exists - module sqlalchemy

Signature de la fonction exists

def exists(*args, **kwargs) 

Description

exists.__doc__

Construct a new :class:`_expression.Exists` construct.

        The :func:`_sql.exists` can be invoked by itself to produce an
        :class:`_sql.Exists` construct, which will accept simple WHERE
        criteria::

            exists_criteria = exists().where(table1.c.col1 == table2.c.col2)

        However, for greater flexibility in constructing the SELECT, an
        existing :class:`_sql.Select` construct may be converted to an
        :class:`_sql.Exists`, most conveniently by making use of the
        :meth:`_sql.SelectBase.exists` method::

            exists_criteria = (
                select(table2.c.col2).
                where(table1.c.col1 == table2.c.col2).
                exists()
            )

        The EXISTS criteria is then used inside of an enclosing SELECT::

            stmt = select(table1.c.col1).where(exists_criteria)

        The above statement will then be of the form::

            SELECT col1 FROM table1 WHERE EXISTS
            (SELECT table2.col2 FROM table2 WHERE table2.col2 = table1.col1)

        .. seealso::

            :ref:`tutorial_exists` - in the :term:`2.0 style` tutorial.