not exists比not in效率要高 |
發(fā)布時間: 2012/8/4 17:02:44 |
數(shù)據(jù)庫:Oracle select * from quyu_t a where a.version='256' and not exists(select 'x' from quyu_t_his b -------用not in效率低- select * from quyu_t where username not in (select username from quyu_t_his) 2個一比較簡直是太明顯了。 本文出自:億恩科技【mszdt.com】 |