CASCADE delete preview in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CASCADE DELETE do in a database?

It automatically deletes all related rows in child tables when a row in the parent table is deleted.

beginner

Why is CASCADE DELETE useful?

It helps keep data consistent by removing dependent records without needing extra queries.

beginner

What happens if you delete a parent row without CASCADE DELETE set on its foreign keys?

The database will prevent the deletion if child rows exist, to avoid orphaned data.

intermediate

How can you preview which rows will be deleted by a CASCADE DELETE?

By running SELECT queries on child tables filtering by the parent row's key before deleting.

intermediate

Write a simple SQL command to create a foreign key with CASCADE DELETE.

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

What does ON DELETE CASCADE do in a foreign key constraint?

A Deletes child rows automatically when parent row is deleted

B Prevents deletion of parent rows if child rows exist

C Deletes parent rows automatically when child row is deleted

D Does nothing on delete

ON DELETE CASCADE means deleting a parent row will also delete all related child rows automatically.

If you want to check which child rows will be deleted by a CASCADE DELETE, what should you do?

A Disable foreign key constraints

B Delete the parent row directly

C Drop the child tables

D Run SELECT queries on child tables filtering by parent key

You preview the effect by selecting child rows linked to the parent before deleting.

What happens if you delete a parent row without ON DELETE CASCADE and child rows exist?

A Deletion fails due to foreign key constraint

B Parent row is updated instead

C Child rows are deleted automatically

D Deletion succeeds and child rows remain

The database blocks deletion to avoid orphaned child rows.

Which SQL clause defines CASCADE DELETE behavior?

A ON UPDATE CASCADE

B ON DELETE CASCADE

C ON DELETE SET NULL

D ON DELETE RESTRICT

ON DELETE CASCADE sets the delete behavior to cascade deletions.

Why should you preview CASCADE deletes before running them?

A To disable foreign keys

B To speed up the deletion

C To avoid accidentally deleting important related data

D To create backups automatically

Previewing helps prevent unintended data loss by showing what will be deleted.

Explain in your own words what CASCADE DELETE does and why it is important.

Think about what happens to connected data when you remove a main record.

Describe how you would preview the rows affected by a CASCADE DELETE before actually deleting.

Imagine checking what will be lost before pressing delete.