Question

表格：

    CREATE TABLE `relation` (
     `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
     `name` varchar(40) NOT NULL,
     `gender` tinyint(1) DEFAULT NULL,
     PRIMARY KEY (`id`),
     UNIQUE KEY `unique_relation` (`name`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8

    CREATE TABLE `invite` (
     `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
     `date_sent` date NOT NULL,
     `user_id` int(10) unsigned NOT NULL,
     `relation_id` int(10) unsigned NOT NULL,
     `email` varchar(255) NOT NULL,
     `code` varchar(255) NOT NULL,
     PRIMARY KEY (`id`),
     KEY `fk_user` (`user_id`),
     CONSTRAINT `fk_user` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8

执行的SQL语句是：

ALTER TABLE `invite` 
ADD CONSTRAINT `fk_relation`  
FOREIGN KEY (`relation_id`) 
REFERENCES `relation` (`id`) 
ON DELETE CASCADE ON UPDATE RESTRICT

Mysql错误：

SQLSTATE[HY000]: General error: 1005 Can't create table 'dbtest.#sql-d00_39' (errno: 121).

relation.id 和 invite.relation_id 列的类型相同int（10）unsigned

更新添加此密钥时，表邀请为空。表关系有3行。

Answer 1

试试这个：

ALTER TABLE invite
ADD CONSTRAINT fk_relation
FOREIGN KEY (relation_id)
REFERENCES relation(id)

根据doc语法是正确的SQL FOREIGN KEY Constraint

Answer 2

外键创建的DDL现在自动包含用于指定“删除”和“更新”操作的语句。但是，对于“删除”，它包含语句“ON DELETE RESTRICT”，它似乎不是有效的T-SQL语句。

尝试这个：



ALTER TABLE invite WITH CHECK ADD CONSTRAINT fk_relation 
FOREIGN KEY (relation_id) REFERENCES relation (id)

为什么我不能这样添加外键约束？

2 个答案: