DELETE trigger in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a DELETE trigger in SQL?

A DELETE trigger is a special kind of stored procedure that automatically runs when a DELETE operation happens on a table. It lets you react to row deletions, like logging or preventing the delete.

beginner

When does a DELETE trigger execute?

A DELETE trigger executes immediately before or after a DELETE statement removes rows from a table, depending on whether it is defined as BEFORE DELETE or AFTER DELETE.

intermediate

What is the difference between BEFORE DELETE and AFTER DELETE triggers?

BEFORE DELETE triggers run before the rows are deleted, allowing you to check or modify data. AFTER DELETE triggers run after the rows are deleted, useful for actions like logging the deletion.

intermediate

How can you access the deleted rows inside a DELETE trigger?

Inside a DELETE trigger, you can access the deleted rows using the special table called OLD (in some SQL dialects) or DELETED (in others), which holds the data of the rows being deleted.

beginner

Why would you use a DELETE trigger in a database?

You use a DELETE trigger to automatically perform tasks like auditing deletions, enforcing business rules, preventing accidental deletes, or cleaning up related data when rows are deleted.

What does a DELETE trigger do?

A Runs automatically when rows are deleted from a table

B Runs when rows are inserted into a table

C Runs when rows are updated in a table

D Deletes a table automatically

A DELETE trigger runs automatically when rows are deleted from a table.

Which special table holds the deleted rows inside a DELETE trigger?

A OLD

B NEW

C CURRENT

D INSERTED

The OLD table holds the data of the rows being deleted inside a DELETE trigger.

When does an AFTER DELETE trigger run?

A Before rows are deleted

B Before rows are inserted

C After rows are updated

D After rows are deleted

An AFTER DELETE trigger runs after the rows have been deleted.

Which of these is NOT a common use of DELETE triggers?

A Logging deleted rows

B Preventing accidental deletes

C Automatically inserting new rows

D Cleaning up related data

DELETE triggers do not automatically insert new rows; they react to deletions.

Can a DELETE trigger modify the data being deleted before it happens?

A No, only INSERT triggers can modify data

B Yes, if it is a BEFORE DELETE trigger

C Yes, but only AFTER DELETE triggers

D No, triggers cannot modify data

BEFORE DELETE triggers can check or modify data before deletion.

Explain what a DELETE trigger is and when it runs.

Think about what happens when you remove rows from a table.

Describe two practical uses of DELETE triggers in a database.

Why would you want to react automatically when data is deleted?