An audit changes on a PostgreSQL table.

pgsql_audit.sql

CREATE TABLE customers_audit AS (
	id SERIAL NOT NULL UNIQUE PRIMARY KEY,
	created TIMESTAMPTZ NOT NULL DEFAULT NOW(),
	before HSTORE,
	after HSTORE
);

CREATE FUNCTION trigger_customers_audit RETURNS TRIGGER LANUAGE plpgsql AS $$
	INSERT INTO customers_audit(before, after)
		SELECT hstore(OLD), hstore(NEW);
	RETURN NEW;
END; $$;

CREATE TRIGGER customers_audit 
AFTER UPDATE ON customers FOR EACH ROW 
EXECUTE PROCEDURE trigger_customers_audit();