SQL语句性能

-- 样例1
select t3.*,t4.emplname from (
       select t2.*,rownum rn from (
              select t.* from t_mcs_mmsinfo t order by t.taskreqtime desc
       ) t2
) t3
left join t_mcs_user t4 on t3.assessorid = t4.userid
where t3.rn > 0 and t3.rn < 100;

-- 样例2
select t4.*,t5.emplname from (
     select * from (
            select t2.*,rownum rn from (
                   select t.* from t_mcs_mmsinfo t order by t.taskreqtime desc
            ) t2
     ) t3
where t3.rn > 0 and t3.rn < 100
) t4
left join t_mcs_user t5 on t4.assessorid = t5.userid;

 

测试结果：上述两SQL语句，执行的时间相同；

结论：在进行表连接时，where条件将优先被执行；

 

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