1. Review of MySQL basic knowledge
Before performing the MySQL cascade delete operation, we need to understand some basic knowledge of MySQL.
1. Characteristics of relational database
Relational database refers to a database that uses tables to organize data. Its characteristics are:
(1) Data is stored in table form, and each table represents an entity type.
(2) The columns in the table represent different attributes, and the rows represent different instances.
(3) Tables can be connected through primary key-foreign key relationships.
2. Keywords
There are many keywords in MySQL, such as: SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, JOIN, etc. These keywords are used to perform different database operations.
3. Basic operations
MySQL has four basic operations: SELECT, INSERT, UPDATE and DELETE. Among them, DELETE is used to delete data in the database, which is the knowledge point we are going to talk about today - cascade deletion.
2. Basic knowledge of MySQL cascade delete
In MySQL, cascade delete mainly involves the issue of foreign key constraints. Foreign keys are used in databases to establish relationships between tables. In order to maintain the integrity and consistency of the data, when there are foreign key constraints, the related slave table records need to be deleted first, and then a record in the master table can be deleted.
1. Foreign key constraints
In a relational database, foreign key constraints are used to maintain associations between tables. In short, two or more tables are connected through foreign keys.
In MySQL, foreign key constraints are mainly divided into two categories: cascade control and restriction control. Cascading control can perform cascading operations on the row where the foreign key is located when performing operations, including cascading updates and cascading deletes.
2. Cascade deletion
In MySQL, when using foreign key constraints, you can set cascade deletion rules to automatically delete slave table records when deleting master table records. It is actually a statement "ON DELETE CASCADE", which will delete all related records from the table to maintain data consistency.
For example, suppose we have two tables: posts and comments. Among them, the posts table has an ID as the primary key, and the comments table has a post_id as a foreign key, which is used to establish an association with the posts table. It looks like this:
posts Form:
ID | Title |
---|---|
1 | Article 1 |
2 | Article 2 |
3 | Article 3 |
comments form:
post_id | Comment content | |
---|---|---|
1 | This is the comment of the first article | |
2 | This is the comment of the second article | |
2 | This is the second comment on the second article | |
3 | This is the comment on the third article |
DELETE FROM posts WHERE ID=1;This command will delete the record with ID 1 in the posts table, and because we have set the cascade deletion rule, all records in the comments table associated with it will also be deleted. will be deleted, and the final result is: posts Form:
Title | |
---|---|
Article 2 | |
Article 3 |
post_id | Comment content | |
---|---|---|
2 | This is the comment of the second article | |
2 | This is the second comment on the second article | |
3 | This is the comment on the third article |
The above is the detailed content of How to use mysql cascade delete function. For more information, please follow other related articles on the PHP Chinese website!

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