select * from t1 inner join t2 on t1.id=t2.ref_id where t1.sip=0select * from
(select * from t1 where t1.sip=0) t3 inner join t2
on t3.id=t2.ref_id
哪种效率高?十分感谢
(select * from t1 where t1.sip=0) t3 inner join t2
on t3.id=t2.ref_id
哪种效率高?十分感谢
调试欢乐多
select * from t1 inner join t2 on t1.id=t2.ref_id where t1.sip=0这个语句,是先过滤t1中t1.sip=0,然后和t2连接,
还是先 t1,t2连接,在这个结果里 过滤t1.sip=0?
或者贴出explain select ..以供大家分析讨论。
拿不定把握,看查询计划。t1.id=t2.ref_id, (似乎是主外键关联),t1.sip上如果没有索引,那第2种就悲剧了。