Shulou(Shulou.com)06/01 Report--

Why did mysql add foreign key errors? This problem may be often seen in our daily study or work. I hope you can gain a lot from this question. The following is the reference content that the editor brings to you, let's take a look at it!

Reasons for errors in adding foreign keys in mysql: 1, the field of the foreign key does not match the type of the associated field; 2, the foreign key name is duplicated; 3, the foreign key is not indexed; 4, there is a default value for the foreign key; 5, syntax error.

Cause analysis:

The first case: the field of the foreign key does not match the type of the associated field (including the mismatch of the encoding format)

The second case: the name of the foreign key is an existing key value, so make sure that the name is unique.

The third case: the foreign key creation caused by the mysql engine cannot be saved or does not work. The general default engine for mysql is myisam, while myisam cannot create foreign keys.

The fourth case: the foreign key you are trying to create is not indexed, or it is not a primary key and if it is not a primary key, you must create an index for it.

The fifth case: the action of the foreign key is set to on delete set null or on update set null, but the no null is set in the field of the associated table, resulting in a conflict.

The sixth case: in the table primary key set by navicat, there is a difference between primary key 1, primary key 2, primary key 3, primary key 1 cannot be cascaded to update (delete) (CASCADE)

The seventh case: there is a default value for foreign keys, resulting in conflicts

The eighth case: if the mixed key value is caused by the lack of index, you need to apply for an index separately for him.

Ninth case: create or alter syntax error when creating foreign keys in sql statement

Thank you for reading! After reading the above, do you have a general idea of why mysql added foreign key errors? I hope the content of the article will be helpful to all of you. If you want to know more about the relevant articles, you are welcome to follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.