"NOT IN", "JOIN...IS NULL", "NOT EXISTS" 之间的效率对比
摘要：
语句一：select count(*) from A where A.a not in (select a from B) 语句二：select count(*) from A left join B on A.a = B.a where B.a is null 语句三：select count(*) from A where not exists (select a from B where... 阅读全文
posted @ 2007-11-20 19:48 焰凌 阅读(838) 评论(3) 推荐(0) 编辑