CASCADE delete preview in SQL

Introduction

CASCADE delete preview helps you see which rows will be removed automatically when you delete a row that has related data in other tables.

When you want to delete a customer and also remove all their orders automatically.

When cleaning up data and you want to know what related records will be deleted.

Before deleting a product to see which sales records will be removed.

When managing parent-child relationships in tables and ensuring no orphan data remains.

Syntax

SQL

SELECT * FROM child_table WHERE foreign_key_column IN (SELECT primary_key_column FROM parent_table WHERE condition);

This query previews child rows linked to parent rows you plan to delete.

Replace child_table, foreign_key_column, parent_table, primary_key_column, and condition with your actual table and column names.

Examples

Shows all orders for customer with id 5 that will be deleted if the customer is deleted with CASCADE.

SQL

SELECT * FROM orders WHERE customer_id IN (SELECT id FROM customers WHERE id = 5);

Previews comments linked to post 10 that will be removed if the post is deleted.

SQL

SELECT * FROM comments WHERE post_id IN (SELECT id FROM posts WHERE id = 10);

Sample Program

This example creates two tables with a CASCADE delete rule. It inserts sample data and previews orders linked to customer 1 before deleting.

SQL

CREATE TABLE customers (id INT PRIMARY KEY, name VARCHAR(50));
CREATE TABLE orders (id INT PRIMARY KEY, customer_id INT, product VARCHAR(50),
  FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE CASCADE);

INSERT INTO customers VALUES (1, 'Alice'), (2, 'Bob');
INSERT INTO orders VALUES (101, 1, 'Book'), (102, 1, 'Pen'), (103, 2, 'Notebook');

-- Preview orders that will be deleted if customer with id=1 is deleted
SELECT * FROM orders WHERE customer_id IN (SELECT id FROM customers WHERE id = 1);

Important Notes

CASCADE delete automatically removes related rows in child tables when a parent row is deleted.

Always preview with a SELECT query before deleting to avoid accidental data loss.

Not all databases support CASCADE delete; check your database documentation.

Summary

CASCADE delete preview shows which related rows will be removed automatically.

Use a SELECT query with IN and a subquery to find child rows linked to parent rows.

Previewing helps protect your data by confirming what will be deleted.