【Mysql】外键

MYSQL数据表建立外键

MySQL创建关联表可以理解为是两个表之间有个外键关系，但这两个表必须满足三个条件

1.两个表必须是InnoDB数据引擎

2.使用在外键关系的域必须为索引型(Index)

3.使用在外键关系的域必须与数据类型相似

例如：

1、建立s_user表

create table s_user(

u_id int auto_increment primary key,

u_name varchar(15),

u_pwd varchar(15),

u_truename varchar(20),

u_role varchar(6),

u_email varchar(30)

)

2、

插入几条数据

参考：https://www.cnblogs.com/ada-zheng/p/3741265.html

insert into s_user values

(1,"wangc","aaaaaa","wangchao","buyer","[e-mail]"),

(2,"huangfp","bbbbbb","huangfp","seller","[e-mail]"),

(3,"zhang3","cccccc","zhangsan","buyer","[e-mail]"),

(4,"li4","dddddd","lisi","seller","[e-mail]")

3、

建立s_orderform表

create table s_orderform(

      o_id int auto_increment primary key,
     o_buyer_id int,
     o_seller_id int,
     o_totalprices double,
     o_state varchar(50),
     o_information varchar(200),
     foreign key(o_buyer_id) references s_user(u_id),      #外链到s_user表的u_id字段
     foreign key(o_seller_id) references s_user(u_id)      #外链到s_user表的u_id字段

)