关于SQL语句提问。
下面两个SQL语句的执行结果有什么区别? (希望能从原理上加以解释,我认为最终执行结果应该一致)
哪个的执行效率会更高?
1
select uniqueNumber from His H left outer join Mth M on H.ondate = M.ondate and H.sno = M.sno and(M.mcode = 100 or M.mcode = 200 or m.mcode = 300)
where M.ondate is null
2
select uniqueNumber from His H left outer join Mth M on H.ondate = M.ondate and H.sno = M.sno where M.ondate is null
and(M.mcode = 100 or M.mcode = 200 or m.mcode = 300)