select T1.*,T2.a from T1,T2 where T1.id=T2.id
t1.id到t2.id 是可以一对多的关系select *,(select a from T2 where id=T1.id) as a from T1
t1.id到t2.id 是不可以一对多的关系
t1.id到t2.id 是可以一对多的关系select *,(select a from T2 where id=T1.id) as a from T1
t1.id到t2.id 是不可以一对多的关系
select *,(select a from T2 where id=T1.id) as a from T1如果就是这两条语句相比,哪个会速度上占优?