1、select name from student s ,achievement a where s.id=a.id and mark>85;
2、select count（*） from achievement where mark>=90;
3、insert into achievement(id,mark) values (1,80);
4、update achievement set Mark=87 where id=(select id from student where name=Rose);
5、delete from student where name='Betty'；
delete from achievement where id=（select id from student where name=Betty）;
update score set score=100 where stu_id=(select id from student where name='张三');
