删除别名问题
delete from aaa where id in (select id from bbb) 对 delete from aaa a where exist(select id from bbb where id=a.id) 错 delete a from aaa a where exist(select id from bbb where id=a.id) 对
两表更新多个字段
update student a,student2 b set a.class_name=b.class_name, a.name=b.name, a.age=b.age where a.id=b.id
异或函数
select BIT_XOR(is_valid) from student group by sname --is_valid两个相同为0,不同为1