Mysql--自关联、子查询

**自关联，表：省份、城市、县级区都有id、name共同属性，可以建立一张卡，
id、name、pid **
查询山东省有哪些城市

select province.name,city.name from areas as province inner join areas as city on city.pid=provice.id having provice.name='山东省';

子查询（速度慢点）

查询最高男生信息
select * from student where height=(select max(height) from student );