trigger

gistfile1.txt

$ CREATE FUNCTION sanitize_dates() RETURNS TRIGGER AS $$
BEGIN
    IF TG_OP = 'INSERT' THEN
        NEW.created_on := now();
        NEW.last_modified := NULL;
    ELSIF TG_OP = 'UPDATE' THEN
        NEW.created_on := OLD.created_on;
        NEW.last_modified := now();
    END IF;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;
$ CREATE TRIGGER sanitize_dates_trg
    BEFORE INSERT OR UPDATE
    ON users
    FOR EACH ROW
    EXECUTE PROCEDURE sanitize_dates();