Check out example codes for "example of trigger in postgresql". It will help you in understanding the concepts better.

Code Example 1

-- Trigger to update donatiom count in donor table whenever
-- A new donation is made by that person

CREATE or REPLACE FUNCTION increase_count()
RETURNS TRIGGER
AS
$$
BEGIN
	UPDATE donor SET dcount = dcount + 1 WHERE did = NEW.did;
END
$$
LANGUAGE plpgsql;



CREATE TRIGGER update_donation_count AFTER INSERT ON donation
FOR EACH ROW
EXECUTE PROCEDURE increase_count();

Learn ReactJs, React Native from akashmittal.com