exists 的应用

SELECT cq.ayxsbh, cq.process_ins_id, nsr.nsrsbh, nsr.nsrmc, jg.swjg_mc
  FROM t03_cqzb cq, t03_ayxsqc ay, dm_swjg jg, dj_nsrxx nsr
 WHERE cq.process_ins_id = 2991
   AND SYSDATE > cq.jzrq
   AND NOT EXISTS (
               SELECT 1
                 FROM t03_cqzb_wc wc
                WHERE wc.process_ins_id = cq.process_ins_id
                      AND wc.lcjsbz = 'Y')
   AND cq.ayxsbh = ay.ayxsbh
   AND ay.nsrsbh = nsr.nsrsbh
   AND ay.lrdw_bm = jg.swjg_dm