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mysql - 如何在现有表中添加外键约束

转载 作者:行者123 更新时间:2023-11-29 01:11:31 25 4
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我有 2 个表,第一个是 smsusers(id,fname,lname,userid)'id' 是主键,userid 是唯一键

address_detail(id,address,type);

这里我想将 smsusersuserid 作为外键添加到 address_detail 表。

为此,我在 address_detail 中添加了一列作为 user_id

ALTER TABLE address_detail add user_id INT( 20 )  default NULL;

现在我正在为表添加外键约束

ALTER TABLE `address_detail` add CONSTRAINT address_detail_fk FOREIGN KEY (user_id) 
REFERENCES smsusers ('userid') ON UPDATE CASCADE ON DELETE CASCADE;

这一步出现以下错误

#1064 - 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 ''userid') ON
UPDATE CASCADE ON DELETE CASCADE' at line 1

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