On Delete Cascade - (MySQL Misc)

In MySQL, the ON DELETE CASCADE option is used to automatically delete records from a child table when a record in the parent table is deleted. In this tutorial, we'll discuss the syntax, example, output, explanation, use, important points, and summary of using ON DELETE CASCADE in MySQL.

Syntax

The basic syntax for using ON DELETE CASCADE in MySQL is as follows:

ALTER TABLE child_table ADD FOREIGN KEY (parent_id) REFERENCES parent_table(id) ON DELETE CASCADE;

This statement adds a foreign key constraint to the "child_table" that references the "id" column in the "parent_table". The ON DELETE CASCADE option is used to specify that when a record in the "parent_table" is deleted, any related records in the "child_table" should also be deleted.

Example

Let's say we have two tables: orders and order_items. The orders table has a primary key column called id, and the order_items table has a foreign key column called order_id that references the id column in the orders table.

If we want to automatically delete any records in the order_items table that are related to a deleted record in the orders table, we can use ON DELETE CASCADE as follows:

ALTER TABLE order_items ADD FOREIGN KEY (order_id) REFERENCES orders(id) ON DELETE CASCADE;

Now, if we delete a record from the orders table, any related records in the order_items table will also be deleted.

Explanation

In the example above, we used ON DELETE CASCADE to automatically delete records from the order_items table when a record in the orders table is deleted. This ensures that the database remains consistent, as any related data in the order_items table is automatically removed when the corresponding record in the orders table is deleted.

Use

Using ON DELETE CASCADE can simplify database management by automatically removing related records when a record in the parent table is deleted. This can ensure that the database remains consistent and avoids the need for manual cleanup operations.

Important Points

• Using ON DELETE CASCADE can cause data loss if not used carefully, so it is important to ensure that related records are correctly identified and shouldn't be retained.
• ON DELETE CASCADE is a faster way to delete records, as it avoids the need for multiple delete statements to remove related records.

Summary

In this tutorial, we discussed how to use ON DELETE CASCADE in MySQL to automatically delete records from a child table when a record in the parent table is deleted. We covered the syntax, example, output, explanation, use, and important points of using ON DELETE CASCADE in MySQL. Understanding this feature can help you manage your database more efficiently and keep it consistent.