mysql外键

1 CREATE TABLE zhujian (
2  id int(11) PRIMARY KEY auto_increment,
3  name varchar(32) default ‘‘);

1 CREATE TABLE waijian (
2  id int(11) PRIMARY KEY auto_increment,
3  zhujian_id int(11) default NULL,
4  name varchar(32) default ‘‘,
5 FOREIGN KEY (zhujian_id) REFERENCES zhujian (id));

1 insert into zhujian (name) values ("xiaostudy");

1 insert into waijian (zhujian_id, name) values (1, "smallstudy");

1 delete from zhujian where id=1;

1 delete from waijian where id=1;

1 alter table waijian add foreign key(zhujian_id) references zhujian(id) on delete cascade on update cascade;