create table track_sal_emp (
    id_emp numeric not null,
    dif_sal numeric
);

create or replace function process_dif_sal() RETURNS TRIGGER AS $new_Emp$
    BEGIN
        if(TG_OP = 'UPDATE') THEN
            insert into track_sal_emp (id_emp, dif_sal)  VALUES(OLD.empno, NEW.sal - OLD.sal);
        END if;
        return null;
    end;
$new_Emp$ LANGUAGE plpgsql;

CREATE TRIGGER chek_dif_sal
AFTER INSERT OR UPDATE OR DELETE ON new_emp
    FOR EACH ROW EXECUTE FUNCTION process_dif_sal();

UPDATE new_Emp
    SET sal = 5000
    where sal between 4000 and 4500;