AFTER trigger behavior in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an AFTER trigger in PostgreSQL?

An AFTER trigger is a database trigger that runs after the triggering SQL statement (INSERT, UPDATE, DELETE) has completed successfully.

beginner

When does an AFTER trigger execute in relation to the triggering SQL statement?

It executes only after the triggering statement has completed successfully.

intermediate

Can an AFTER trigger modify the data of the triggering statement in PostgreSQL?

No, AFTER triggers cannot modify the data of the triggering statement because they run after the statement completes.

intermediate

What happens if an AFTER trigger raises an error in PostgreSQL?

If an AFTER trigger raises an error, the entire transaction is rolled back, including the original statement and any other changes.

intermediate

Why would you use an AFTER trigger instead of a BEFORE trigger?

Use AFTER triggers when you want to perform actions that depend on the statement being successfully completed, such as logging or cascading changes.

When does an AFTER trigger run in PostgreSQL?

A After the triggering statement completes successfully

B At the same time as the triggering statement

C Before the triggering statement executes

D Only if the triggering statement fails

AFTER triggers run only after the triggering statement has completed successfully.

Can an AFTER trigger modify the row data being inserted or updated?

A Yes, it can modify the data before insertion

B Only if the trigger is a BEFORE trigger

C Yes, but only for DELETE statements

D No, it runs after the data is already changed

AFTER triggers run after the data change, so they cannot modify the row data of the triggering statement.

What happens if an AFTER trigger raises an error during execution?

A The entire transaction is rolled back

B Only the trigger action is rolled back

C The error is ignored and the transaction commits

D The trigger retries automatically

An error in an AFTER trigger causes the entire transaction to roll back.

Which of the following is a common use case for AFTER triggers?

A Modifying data before update

B Logging changes after data modification

C Validating data before insert

D Preventing deletes

AFTER triggers are often used for logging or actions that depend on successful completion of the statement.

In PostgreSQL, can an AFTER trigger be fired for a statement that fails?

A Yes, always

B Only for DELETE statements

C No, only if the statement succeeds

D Only if the trigger is set to fire on error

AFTER triggers only fire if the triggering statement completes successfully.

Explain the behavior and timing of an AFTER trigger in PostgreSQL.

Think about when the trigger runs and what it can or cannot do.

Describe scenarios where using an AFTER trigger is more appropriate than a BEFORE trigger.

Consider what you want to do after data is safely changed.