Trigger execution order in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a trigger in PostgreSQL?

A trigger is a special procedure that automatically runs when certain events happen in the database, like inserting, updating, or deleting data.

intermediate

When multiple triggers are set on the same event, how does PostgreSQL decide which trigger runs first?

PostgreSQL executes BEFORE triggers in alphabetical order by their names before the event, and AFTER triggers in alphabetical order by their names after the event.

beginner

What is the difference between BEFORE and AFTER triggers in execution order?

BEFORE triggers run before the database action happens, and they run in alphabetical order. AFTER triggers run after the action and run in alphabetical order.

intermediate

Can you control the order of trigger execution in PostgreSQL?

You can control the order by naming triggers carefully because PostgreSQL orders both BEFORE and AFTER triggers alphabetically by name.

beginner

What happens if two triggers have the same name in PostgreSQL?

PostgreSQL does not allow two triggers with the same name on the same table. Each trigger must have a unique name per table.

In PostgreSQL, which triggers run first on an INSERT event?

A BEFORE triggers in alphabetical order

B AFTER triggers in alphabetical order

C BEFORE triggers in reverse alphabetical order

D AFTER triggers in reverse alphabetical order

BEFORE triggers run before the event and are executed in alphabetical order by their names.

How are AFTER triggers executed in PostgreSQL?

A Randomly

B In reverse alphabetical order

C In the order they were created

D In alphabetical order

AFTER triggers run after the event and are executed in alphabetical order by their names.

Can you have two triggers with the same name on the same table and event in PostgreSQL?

A Yes, if they are BEFORE and AFTER triggers

B No, trigger names must be unique per table

C Yes, if they have different functions

D Yes, if they are on different columns

Trigger names must be unique for each table.

If you want a trigger to run last among BEFORE triggers, how should you name it?

A Start its name with 'Z'

B Use numbers in the name

C Name does not affect order

D Start its name with 'A'

BEFORE triggers run in alphabetical order, so a name starting with 'Z' will run last.

Which of these is true about trigger execution order in PostgreSQL?

A AFTER triggers run before BEFORE triggers

B BEFORE triggers run after the event

C BEFORE triggers run before the event in alphabetical order

D Trigger execution order is random

BEFORE triggers run before the event and are executed in alphabetical order.

Explain how PostgreSQL decides the order of trigger execution when multiple triggers exist on the same event.

Think about the timing (before or after) and the alphabetical order of trigger names.

Describe how you can control the execution order of triggers in PostgreSQL.

Focus on naming triggers to influence their order.