postgresql – Triggers and Trigger Functions – Basic PL/pgSQL Trigger Function

This is a simple trigger function.

CREATE OR REPLACE FUNCTION my_simple_trigger_function()
RETURNS trigger AS
$BODY$

BEGIN
    -- TG_TABLE_NAME :name of the table that caused the trigger invocation
IF (TG_TABLE_NAME = 'users') THEN

    --TG_OP : operation the trigger was fired
  IF (TG_OP = 'INSERT') THEN 
    --NEW.id is holding the new database row value (in here id is the id column in users table)
    --NEW will return null for DELETE operations
    INSERT INTO log_table (date_and_time, description) VALUES (now(), 'New user inserted. User ID: '|| NEW.id);        
    RETURN NEW;        

  ELSIF (TG_OP = 'DELETE') THEN    
    --OLD.id is holding the old database row value (in here id is the id column in users table)
    --OLD will return null for INSERT operations
    INSERT INTO log_table (date_and_time, description) VALUES (now(), 'User deleted.. User ID: ' || OLD.id);
    RETURN OLD;        
    
  END IF;

RETURN null;
END IF;

END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;

Adding this trigger function to the users table

CREATE TRIGGER my_trigger
AFTER INSERT OR DELETE
ON users
FOR EACH ROW
EXECUTE PROCEDURE my_simple_trigger_function();

if you want to reproduce, please indicate the source:
postgresql – Triggers and Trigger Functions – Basic PL/pgSQL Trigger Function - CodeDay