SQL中IN和EXISTS用法的区别
摘要:
NOT INSELECT DISTINCT MD001 FROM BOMMD WHERE MD001 NOT IN (SELECT MC001 FROM BOMMC)NOT EXISTS,exists的用法跟in不一样,一般都需要和子表进行关联,而且关联时,需要用索引,这样就可以加快速度select DISTINCT MD001 from BOMMD WHERE NOT EXISTS (SELECT MC001 FROM BOMMC where BOMMC.MC001 = BOMMD.MD001)exists是用来判断是否存在的,当exists(查询)中的查询存在结果时则返回真,否则返回假。n 阅读全文
posted @ 2013-08-05 10:26 zhangzhan 阅读(165) 评论(0) 推荐(0) 编辑