In PostgreSQL, if you want to set current timestamp as default value, you can simply keep a column’s default expression as now(). However, by default there is no function defined to update the timestamp when a particular row (or multiple rows) need to be updated.

In such scenario, you may create your custom method and trigger it using PostgreSQL’s Triggers. Following snippet will make it more clear:

Here, we are creating a new method, method_get_updated_at()

CREATE OR REPLACE FUNCTION method_get_updated_at() RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
    BEGIN
      NEW.<column_name> = now();
      RETURN NEW;
    END;
$$;

Once it is created, use the following snippet to trigger it:

CREATE TRIGGER trigger_<column_name>
BEFORE UPDATE ON <table_name>
FOR EACH ROW
EXECUTE PROCEDURE method_get_updated_at();

If you want to delete a Trigger, you can use this simple query:

DROP TRIGGER IF EXISTS trigger_<column_name> ON <table_name>

Note: Please update the and accordingly and execute the code for your particular database. Also, note that, some web frameworks (like Rails) manage such columns(created_at, updated_at) automatically.

ALso, if you want to view all existing methods, run this query:

SELECT  p.proname
FROM    pg_catalog.pg_namespace n
JOIN    pg_catalog.pg_proc p
ON      p.pronamespace = n.oid
WHERE   n.nspname = 'public'

And, run this query to view all Triggers:

SELECT * FROM pg_trigger;

Thanks!