Function check_constant_qual

src/backend/executor/nodeMergejoin.c:557–572

* Check that a qual condition is constant true or constant false. * If it is constant false (or null), set *is_const_false to true. * * Constant true would normally be represented by a NIL list, but we allow an * actual bool Const as well. We do expect that the planner will have thrown * away any non-constant terms that have been ANDed with a constant false. */

 * away any non-constant terms that have been ANDed with a constant false.
 */
static bool
check_constant_qual(List *qual, bool *is_const_false)
{
	ListCell   *lc;

	foreach(lc, qual)
	{
		Const	   *con = (Const *) lfirst(lc);

		if (!con || !IsA(con, Const))
			return false;
		if (con->constisnull || !DatumGetBool(con->constvalue))
			*is_const_false = true;
	}
	return true;
}


/* ----------------------------------------------------------------