1、新建主键table
create table demo1_zhujian (
id int primary key auto_increment,
name varchar(10));
2、新建外键table
create table demo2_waijian (
id int primary key auto_increment,
_id int not null default 0,
name varchar(10),
index (_id),
FOREIGN KEY (_id) REFERENCES demo1_zhujian(id) ON DELETE CASCADE ON UPDATE CASCADE);
create table demo3_waijian (
id int primary key auto_increment,
_id int not null default 0,
name varchar(10),
index (_id),
FOREIGN KEY (_id) REFERENCES demo1_zhujian(id) ON DELETE CASCADE ON UPDATE CASCADE);
3、添加数据
insert into demo1_zhujian
(name)
values
('');
insert into demo2_waijian
(_id, name)
values
(1, 'demo2_1');
insert into demo3_waijian
(_id, name)
values
(1, 'demo3_1');
4、查询数据
select * from demo1_zhujian;
select * from demo2_waijian;
select * from demo3_waijian;
5、修改主键数据
update demo1_zhujian set id=22 where id=1;
6、重复第4步
外键table中修改外键不行
7、主键table中删除数据
delete from demo1_zhujian where id=22;
8、重复第4步
