MySQL级联删除和级联修改

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

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