Function is_exprs_nullable

src/backend/cdb/cdbsubselect.c:1401–1419

* is_exprs_nullable * Return true if any of the exprs might be null, otherwise false. * We want to be conservative for those cases either we are not * interested or not sure. */

 *   interested or not sure.
 */
static bool
is_exprs_nullable(Node *exprs, Query *query)
{
	NonNullableVarsContext context;
	context.query           = query;
	context.nonNullableVars = NIL;
	context.nullableVars = NIL;

	/* Find nullable vars in the jointree */
	(void) expression_tree_walker((Node *) query->jointree,
								  cdb_find_nonnullable_vars_walker, &context);

	/*
	 * Eliminate potential nullable vars.
	 */
	context.nonNullableVars = list_difference(context.nonNullableVars, context.nullableVars);

	return is_exprs_nullable_internal(exprs, context.nonNullableVars);
}

static bool
is_exprs_nullable_internal(Node *exprs, List *nonnullable_vars)