标签：warning 存在 注意 ssi har 成功 inf alter cat
1，外键补充，一提到外键，肯定最少存在两张表的关系，外键有几个写几个就好
2，创建表的时候，最后一行不要加逗号，不然会报错的
mysql> create table userinfo( -> id int not null auto_increment primary key, -> name varchar(10), -> department_id int, -> ) engine=innodb default charset=utf8; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘) engine=innodb default charset=utf8‘ at line 5
3，两张表，创建简单的外键关系，这个报错的原因是因为department 表里面的id 不是唯一索引的，这个在后面会讲的我记忆当中
mysql> create table department( -> id int not null, -> department char(20) -> ) engine = innodb default charset utf8 -> ; Query OK, 0 rows affected, 1 warning (0.01 sec)
mysql> create table userinfo2( -> id int not null auto_increment primary key, -> name varchar(10), -> department_id int, -> constraint fk_1 foreign key (department_id) references department(id) -> ) engine=innodb default charset=utf8; ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint ‘fk_1‘ in the referenced table ‘department‘
4，所以应用上一小节学习的知识，修改department表里面的ID属性，正确写法如下，注意modify后面没有colume:
mysql> alter table department modify id int not null auto_increment primary key; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0
5，修改完成之后，再次建立外键关系，成功！
mysql> create table userinfo2( id int not null auto_increment primary key, name varchar(10), department_id int, constraint fk_1 foreign key (department_id) references department(id) ) engine=innodb default charset=utf8; Query OK, 0 rows affected, 1 warning (0.01 sec)
6，做一下老师上节课的作业，创建出学生，老师，课程，成绩表，并建立约束关系
标签：warning 存在 注意 ssi har 成功 inf alter cat
原文地址：https://www.cnblogs.com/lisa-blog/p/10349216.html
