MYSQL資料表建立外來鍵

MySQL建立關聯表可以理解為是兩個表之間有個外來鍵關係，但這兩個表必須滿足三個條件
1.兩個表必須是InnoDB資料引擎
2.使用在外來鍵關係的域必須為索引型(Index)
3.使用在外來鍵關係的域必須與資料型別相似

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、

插入幾條資料

insert into s_user values
       (1,"wangc","aaaaaa","wangchao","buyer","[email protected]"),
      (2,"huangfp","bbbbbb","huangfp","seller","[email protected]"),
      (3,"zhang3","cccccc","zhangsan","buyer","[email protected]"),
      (4,"li4","dddddd","lisi","seller","[email protected]")

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),      #外鏈到s_user表的u_id欄位
         foreign key(o_seller_id) references s_user(u_id)      #外鏈到s_user表的u_id欄位
)