mysql 练习 exercise2：虚拟表格并连接

use exercise;

create table dic_area(
    id int(1),
    area_id int(6),
    area_name varchar(10),
    parented int(6),
    area_level int(1));

insert into dic_area values
(1,130000,"河北省",100000,1),
(2,130100,"石家庄市",130000,2),
(3,130102,"长安区",130100,3),
(4,130104,"桥西区",130100,3);


select 
    省份表.area_id as 省代码,
    省份表.area_name as 省名称,
    城市表.area_id as 市代码,
    城市表.area_name as 市名称,
    县级表.area_id as 县代码,
    县级表.area_name as 县名称 
from dic_area as 省份表
inner join dic_area as 城市表 on 省份表.area_id=城市表.parented
inner join dic_area as 县级表 on 城市表.area_id=县级表.parented;

-- 首先用as命名方式虚拟三张表出来，然后省级表和城市表连接最后连接县级表，再选取想要的字段as重命名，中间报错则一条一条添加和排查