以下三张表
student（id,sex,gender,age）
subject(sid,name)
score(id sid score)
update socre set score='score+10' where id in(select id from age>18)
delete from socroe WHERE `id` IN (SELECT `id` FROM sutudent WHERE `age` > 18) AND `cid` IN (SELECT `cid` FROM `score` WHERE `name`='x')
