ALTER TABLE INVOICE
  ADD INV_INFO /* VARCHAR(75) */ COMPUTED BY ('№' || INV_NUM || ' от ' || (select DS from sp_format_date(INV_DATE)));

ALTER TABLE INVOICE
  ADD BALANCE /* NUMERIC(18,2) */ COMPUTED BY (SUM_INVOICE - coalesce(SUM_ACCEPTED, 0)
            - coalesce(SUM_MEK, 0)
            - coalesce(SUM_MEE, 0)
            - coalesce(SUM_EKMP, 0));