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This article mainly introduces the relevant knowledge of what you should pay attention to when using foreign key in mysql, the content is detailed and easy to understand, the operation is simple and fast, and it has a certain reference value. I believe you will gain something after reading this mysql article. Let's take a look at it.

1. To constrain a field in a table, it must be a value that exists in a field in another table.

2. In another table, this column is not necessarily a primary key, but it must be a unique index, otherwise creation will fail.

Example

Mysql > create table orders (id int (11) primary key, userId int (11), FOREIGN KEY (userId) REFERENCES user (id)); Query OK, 0 rows affected, 2 warnings (0.06 sec) mysql > insert orders values (1Magol 3); ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`t`.`orders`, CONSTRAINT `orders_ibfk_ 1` FOREIGN KEY (`userId`) REFERENCES `user` (`id`) mysql > insert orders values (1Pol 1) Query OK, 1 row affected (0.01sec) this is the end of the article on "what to pay attention to when using foreign key in mysql". Thank you for reading! I believe that everyone has a certain understanding of the knowledge of "what should be paid attention to when using foreign key in mysql". If you want to learn more knowledge, you are welcome to follow the industry information channel.

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