elements.py 文件源码

def __init__(self, element, *order_by):
        """Produce a :class:`.WithinGroup` object against a function.

        Used against so-called "ordered set aggregate" and "hypothetical
        set aggregate" functions, including :class:`.percentile_cont`,
        :class:`.rank`, :class:`.dense_rank`, etc.

        :func:`~.expression.within_group` is usually called using
        the :meth:`.FunctionElement.within_group` method, e.g.::

            from sqlalchemy import within_group
            stmt = select([
                department.c.id,
                func.percentile_cont(0.5).within_group(
                    department.c.salary.desc()
                )
            ])

        The above statement would produce SQL similar to
        ``SELECT department.id, percentile_cont(0.5)
        WITHIN GROUP (ORDER BY department.salary DESC)``.

        :param element: a :class:`.FunctionElement` construct, typically
         generated by :data:`~.expression.func`.
        :param \*order_by: one or more column elements that will be used
         as the ORDER BY clause of the WITHIN GROUP construct.

        .. versionadded:: 1.1

        .. seealso::

            :data:`.expression.func`

            :func:`.expression.over`

        """
        self.element = element
        if order_by is not None:
            self.order_by = ClauseList(
                *util.to_list(order_by),
                _literal_as_text=_literal_as_label_reference)