mysql 级联删除

create table a
(
 id  varchar(20) primary key,
 password varchar(20) not null
)

create table b
(
 id int identity(1,1)  primary key,
 name varchar(50) not null,
 userId varchar(20),
 foreign key (userId) references a(id) on delete cascade
)
表B创建了外码userId 对应A的主码ID，声明了级联删除

或者

alter table  b 
add constraint fk_b_userId foreign key (userId) references a(id) on delete cascade

测试数据： insert into a values ('11','aaa') insert into a values('23','aaa') insert into b values('da','11') insert into b values('das','11') insert into b values('ww','23') 删除A表内id为‘11’的数据，发现B表内userId 为“11”也被数据库自动删除了，这就是级联删除 delete from a where id='11'

 

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