这个查询有什么问题（选择为RES1 Union选择param IN（RES1）的位置

The query:

SELECT ct_cid as level1 FROM cat_tree WHERE ct_sid=$sid_int AND ct_parent =$cid_int) UNION (SELECT ct_cid as level2 FROM cat_tree WHERE ct_sid=$sid_int AND ct_parent IN level1)SELECT ct_cid as level1 FROM cat_t