sql--级联删除

参考：https://www.cnblogs.com/fengyingwang/p/3391106.html

实证：

代码如下：

drop table a; 
create table a
(
id  int primary key auto_increment,
user varchar(20) not null
); 

drop table c; 
create table c
(
id  int primary key auto_increment,
groups varchar(20) not null
); 

drop table b; 
create table b
(
id int  primary key auto_increment,
userid int,
groupid int,
foreign key (userid) references a(id) on delete cascade,
foreign key (groupid) references c(id) on delete cascade
); 
 

insert into a(user) values("sddd");
insert into a(user) values("sddd2");
insert into a(user) values("sddd3");

insert into c(groups) values("dddd");
insert into c(groups) values("dddd2");
insert into c(groups) values("dddd3");

insert into b(userid, groupid) values(1,1);
insert into b(userid, groupid) values(1,2);
insert into b(userid, groupid) values(1,3);
insert into b(userid, groupid) values(2,1);
insert into b(userid, groupid) values(2,2);
insert into b(userid, groupid) values(2,3);

delete from c where id=1;
delete from c where id=1;

结果图：