摘要:
1.不为空 select * from table where id <> ""; select * from table where id != ""; select * from table where is not null; 2.为空 select * from table where id 阅读全文
摘要:
1、EXISTS=IN,意思差不多相同,但是语法上有一点不同,好像使用IN效率要差点,应该是不会执行索引的原因 1 SELECT ID,NAME FROM A WHERE ID IN (SELECT AID FROM B WHERE A.ID=B.AID)2 SELECT ID,NAME FROM 阅读全文