MySql工作台: add Foreign key error

Question

我试图在教程表中添加外键“USERNAME”，但出现错误。

Executing:
ALTER TABLE `databse`.`tutorial`   
ADD CONSTRAINT `USERNAME`
   FOREIGN KEY (`USERNAME`)
   REFERENCES `databse`.`register` (`USERNAME`)
   ON DELETE CASCADE
   ON UPDATE CASCADE;

 Operation failed: There was an error while applying the SQL script to the database.
 ERROR 1452: Cannot add or update a child row:
a foreign key constraint   fails (`databse`.`#sql-e7c_5`, CONSTRAINT `USERNAME` FOREIGN KEY (`USERNAME`) 
 REFERENCES `register` (`USERNAME`) ON DELETE CASCADE ON UPDATE CASCADE)
 SQL Statement:
  ALTER TABLE `databse`.`tutorial`  
  ADD CONSTRAINT `USERNAME`
  FOREIGN KEY (`USERNAME`)
  REFERENCES `databse`.`register` (`USERNAME`)
  ON DELETE CASCADE
  ON UPDATE CASCADE

外键设置:

教程表设置:

有什么想法吗？谢谢你

我解决了这个问题，我创建了一个新的“教程”表替换“教程”表，并使用相同的方式添加外键，它起作用了! = =

还是谢谢你的帮助!!

Answer 1

如上所述here :

A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.

在您显示的代码中:您尝试引用“USERNAME”列，这不是上次捕获中的主键

因此，您可以将 register 表中的主键更改为 USERNAME，也可以将外键更改为引用 TutorialName