mySql優化in查詢

普通查詢:

select t1.name,t1.age from table1 t1 
where t1.sid in
(
    select t2.id from table2 t2 where t2.yahei='嘿嘿'
 )

優化后sql

select t1.name,t1.age from table1 t1 
where t1.sid in
(
    select t21d from
    (
        select t2.id as t21d from table2 t2 where t2.yahei='嘿嘿'
    ) as t21d
)