一次sql优化的记录

select a.band,a.name from radio as a where exists ( select radio.id from radio,(select radio_nj.radio_id as radio_id from user,radio_nj where user.role != 5 and user.id = radio_nj.user_id) as b where radio.id = b.radio_id )

select a.band,a.name from radio as a where a.id in (select radio_nj.radio_id from user,radio_nj where user.role != 5 and user.id = radio_nj.user_id);

同样的效果，前面那条只需要0.5秒 后面那条半天没有没出来