create or replace TRIGGER trigger_services
   AFTER UPDATE OF id_tariff ON services
   FOR EACH ROW
DECLARE 
  Q date;
  qq VARCHAR2(1000);
BEGIN    
select v.date_start into q
     from services s
     LEFT JOIN validity_period v ON (s.id_services=v.id_services and s.id_abonent=v.id_abonent)
      where s.id_services=1 and s.id_abonent=1;

qq:= 'INSERT INTO arhif_tariff select new.ID_tariff,  new.id_services,new.id_abonent,new.date_smeni_teriff,Q FROM DUAL';
EXECUTE IMMEDIATE qq ;
END;

create or replace TRIGGER trigger_services
AFTER UPDATE of id_tariff ON services
FOR EACH ROW
BEGIN
   IF :NEW.id_tariff != :old.id_tariff
   THEN
      INSERT INTO arhif_tariff (ID_tariff, id_services,id_abonent,date_smeni_teriff,data_start)
         select s.id_tariff,s.id_services,s.id_abonent,sysdate,v.date_start
         from services s
         LEFT JOIN validity_period v ON (s.id_services=v.id_services and s.id_abonent=v.id_abonent)
         where s.id_services=1 and s.id_abonent=1;
   END IF;
END  trigger_services;