下面2个sql结果一样吗？sql1只是先过滤在update，比sql2性能更好？
--sql1
update t1 a
set a.sal =
(select b.sal from t2 b where b.empno = a.empno)
where exists (select 'x' from t2 b where b.empno = a.empno);
--sql2
update t1 a
s ...
↧