mysql 常见查询优化别优化错了

explain select A.realname,sdept.deptname from
(
select * from syberos_userinfo where realname like '李%' 

) as A left join syberos_employees as sem on A.userid=sem.userid  left join syberos_departments as sdept on sem.deptid=sdept.deptid

explain select A.realname,sdept.deptname from syberos_userinfo as A 
left join syberos_employees as sem on A.userid=sem.userid  left join syberos_departments as sdept on sem.deptid=sdept.deptid where A.realname like '李%' 

上面那个看似优化了，但是没有优化效果，因为当中产生了派生表，派生表之慢很