mysql - mysql单查询如何删除有外键约束的记录

Question

DELETE logins, roles 
FROM logins
INNER JOIN roles ON logins.`LOGIN_ID`=roles.`LOGIN_ID`
WHERE roles.`LOGIN_ID`=25774;

Query: DELETE logins, roles FROM logins INNER JOIN roles ON logins.LOGIN_ID=roles.LOGIN_ID WHERE roles.LOGIN_ID=25774

Error Code: 1451 Cannot delete or update a parent row: a foreign key constraint fails (foodapp.roles, CONSTRAINT roles_ibfk_1 FOREIGN KEY (LOGIN_ID) REFERENCES logins (LOGIN_ID))

Execution Time : 0 sec Transfer Time : 0 sec Total Time : 0.038 sec

Answer 1

如果您没有 ON CASCADE DELETE 约束设置，则需要先从子表中删除该行。然后，触发一个单独的查询以将其从父表中删除。

DELETE FROM roles 
WHERE roles.`LOGIN_ID`=25774;

然后从父表中删除:

DELETE FROM logins
WHERE logins.`LOGIN_ID`=25774;

来自Documentation :

If you use a multiple-table DELETE statement involving InnoDB tables for which there are foreign key constraints, the MySQL optimizer might process tables in an order that differs from that of their parent/child relationship. In this case, the statement fails and rolls back. Instead, you should delete from a single table and rely on the ON DELETE capabilities that InnoDB provides to cause the other tables to be modified accordingly.

<小时/>

如果外键定义中使用了ON CASCADE DELETE，那么您只需从父表中删除即可。它将自动从子表中删除相应的行。