MYSQL的数据表与数据表之间 的外键 和主键 是如何建立链接的呢

Question

如题所述

Answer 1

alter table (主表名)major_info add constraint FK_department_major
foreign key(department_id) references (外键表)department_info(Id)

Answer 2

和sql一样，我写了一个语句
create database dataTest;
use dataTest;
create table testaa
(
testId int primary key auto_increment,--auto_increment:标识列
title varchar(255),
testDate datetime --日期格式
);
create table testbb(
tebb int primary key,
title varchar(200),
testId int,
foreign key (testId) references testaa(testId)
);