mysql - 外键语法

Question

我先创建了Teacher表，它的描述是

   mysql> desc teacher;
   +--------------+-------------+------+-----+---------+-------+
   | Field        | Type        | Null | Key | Default | Extra |
   +--------------+-------------+------+-----+---------+-------+
   | TEACHER_ID   | varchar(3)  | NO   | PRI | NULL    |       |
   | TEACHER_NAME | varchar(40) | YES  |     | NULL    |       |
   +--------------+-------------+------+-----+---------+-------+

我创建了一个新表后如下。我的需要是在下表中我想使用TEACHER_ID作为外键。我写了以下内容。我不知道它是否错误在句法上意味着。但我没有收到任何错误...

 mysql> CREATE TABLE SUB_MCA_TY
->  (SUB_ID VARCHAR(4) PRIMARY KEY,
->  SUB_NAME VARCHAR(30),
-> TEACHER_ID VARCHAR(3) REFERENCES TEACHER(TEACHER_ID));

Answer 1

“内联”外键总是被 MySQL 默默地忽略，即使是 InnoDB(欢迎来到 MySQL 美妙的一致世界......)

您需要将其更改为列后的显式约束:

CREATE TABLE SUB_MCA_TY
(
   SUB_ID VARCHAR(4) PRIMARY KEY,
   SUB_NAME VARCHAR(30),
   TEACHER_ID VARCHAR(3),
   foreign key (TEACHER_ID) REFERENCES TEACHER(TEACHER_ID)
);

Quote from the manual :

MySQL does not recognize or support “inline REFERENCES specifications” (as defined in the SQL standard) where the references are defined as part of the column specification