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This article mainly introduces the use of MySQL foreign keys, has a certain reference value, friends in need can refer to. I hope you will learn a lot after reading this article. Next, let the editor take you to learn about it.

The method of using MySQL foreign key: 1, two tables must be InnoDB table type; 2, the field used in foreign key relationship must be indexed Index;3, and the field used in foreign key relationship must be similar to data type.

Methods for using MySQL foreign keys:

1. Only tables of type InnoDB can use foreign keys. Mysql defaults to MyISAM. This type does not support foreign key constraints.

2, the benefits of foreign keys: can make two tables associated, ensure data consistency and achieve some cascading operations.

3. The role of foreign keys:

The main purpose of maintaining data consistency and integrity is to control the data stored in the foreign key table. Associate the two tables, and the foreign key can only refer to the values of the columns in the table.

4. The premise of establishing foreign keys:

Both tables must be of the InnoDB table type.

Fields used in foreign key relationships must be indexed (Index).

Fields used in foreign key relationships must be similar to data types.

5. Steps to create

Specify the primary key keyword: foreign key (column name).

Reference foreign key keyword: references (foreign key column name).

6. Event trigger limit: on delete and on update. You can set the parameter cascade (follow the foreign key change).

Restrict (restrict foreign key changes in appearance), set

Null (set null), set Default (set default).

[default] no action

7. Give an example

OutTable table primary key id type int

Create a table that contains foreign keys:

The code is as follows:

Create table temp (id int,namechar (20), foreign key (id) references outTable (id) on delete cascade on updatecascade)

Description: set the id column as the foreign key reference id column of the external outTable as the value of the foreign key delete the corresponding column in this table when the value of the foreign key changes the corresponding column value in this table.

The code is as follows:

Create table temp (id int, name char (20), foreign key (id) references outTable (id) on delete cascade on updatecascade); Thank you for reading this article carefully. I hope it will be helpful for the editor to share the usage of MySQL external keys. At the same time, I also hope that you will support us, pay attention to the industry information channel, and find detailed solutions waiting for you to learn.

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