BEFORE trigger behavior in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a BEFORE trigger in PostgreSQL?

A BEFORE trigger is a special function that runs automatically before an INSERT, UPDATE, or DELETE operation on a table. It can modify or check data before the change happens.

beginner

When does a BEFORE trigger execute?

It executes just before the data modification statement (INSERT, UPDATE, DELETE) is applied to the table, allowing changes or checks before the data is saved.

intermediate

Can a BEFORE trigger modify the data being inserted or updated?

Yes, a BEFORE trigger can change the data values before they are saved to the table. For example, it can adjust a column value or reject the operation.

intermediate

What happens if a BEFORE trigger raises an exception?

If a BEFORE trigger raises an exception, the data modification is canceled and the error is returned to the user. This can be used to enforce rules or validations.

beginner

How does a BEFORE trigger differ from an AFTER trigger?

A BEFORE trigger runs before the data change happens and can modify or stop it. An AFTER trigger runs after the change is done and cannot modify the data being changed.

When does a BEFORE trigger run in PostgreSQL?

A After the data modification statement executes

B Before the data modification statement executes

C Only during SELECT queries

D Only when the database starts

A BEFORE trigger runs before the INSERT, UPDATE, or DELETE operation modifies the table.

Can a BEFORE trigger change the data being inserted?

A Yes, it can modify the data before saving

B Only after the data is saved

C Only if the data is numeric

D No, it can only read data

BEFORE triggers can modify the data before it is saved to the table.

What happens if a BEFORE trigger raises an error?

A The data change proceeds anyway

B The error is ignored

C The database restarts

D The data change is canceled

Raising an error in a BEFORE trigger stops the data modification and returns the error.

Which SQL operations can a BEFORE trigger be attached to?

A INSERT, UPDATE, DELETE

B SELECT only

C CREATE and DROP

D ALTER only

BEFORE triggers are used with INSERT, UPDATE, and DELETE operations.

How does a BEFORE trigger differ from an AFTER trigger?

A Both run at the same time

B BEFORE triggers run after data changes; AFTER triggers run before

C BEFORE triggers run before data changes; AFTER triggers run after

D BEFORE triggers only run on SELECT

BEFORE triggers run before the data change, allowing modification; AFTER triggers run after the change.

Explain what a BEFORE trigger does and when it runs in PostgreSQL.

Think about what happens before saving data to a table.

Describe how a BEFORE trigger can affect data integrity or validation.

Consider how you might stop bad data from entering your table.