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Mastering PostgreSQL Databases: From Basics to Advanced

Triggers

Explore how to create and use triggers in PostgreSQL to automatically execute functions in response to data changes. Understand trigger types, event conditions, and reference variables that allow you to maintain data integrity, automate updates, and manage cascading actions efficiently.

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Triggers in PostgreSQL allow executing a function or block of code in response to specific events, such as an insert, update, or delete operations on a table. These triggers can enforce data integrity, perform cascading actions on related tables, and even send notifications. Triggers can’t be called or executed directly—they can only be fired in response to a specific event.

Creating a trigger

To create a trigger, the CREATE TRIGGER statement specifies the triggering event, the function or code block to execute, and optionally, a condition for when the trigger should fire. Triggers can also be modified or dropped using the ALTER TRIGGER and DROP TRIGGER statements, respectively.

PostgreSQL
CREATE TRIGGER <trigger_name> 
AFTER/BEFORE <event> ON <table_name> 
    FOR EACH ROW    
        EXECUTE PROCEDURE <function_name>();

Here, <trigger_name> is the trigger’s name, the triggering event such as insert or update,
the table on which the trigger will operate, and the function or code ...