sql查询——子查询

 -- 子查询
       -- 一句查询语句内，再套一句查询语句 ，叫子查询
       -- 查询班级类身高最高的人的名字
       select name from students where high=(select max(high) from students);
       select id as "序号", name as "姓名",high as "身高" from students where high=(select max(high) from students) order by id desc;
       -- 查询省份下的所有区市，不知道省份的id
       select name from china pid=(select id from china where name="四川省");