try each of these procedures and use the following with the faster,
(I mean, the less slowly).
then
select sum(a.cznetto*a.ilosc),t.KODKRESKO,m.OPIS,...
from sp_X a left join T
on a.idtow=t.id
left join M
on a.idmag=m.id
group by t.KODKRESKO,m.OPIS...


CREATE PROCEDURE sp_X RETURNS
(Z_ID BIGINT,
IDMAG BIGINT,
IDTOW BIGINT,
ILOSC DECIMAL(18,3),
CZNETTO DECIMAL(18,4),
CZNETTO DECIMAL(18,4),
CSBRUTTO DECIMAL(18,4)
)
AS
BEGIN
FOR SELECT Z.ID, Z.IDMAG
FROM SPRZEDAZ Z
WHERE Z.DATASPRZEDAZY BETWEEN '2005-02-01' AND '2005-02-01'
AND ((Z.GODZINA BETWEEN 8 AND 8) OR Z.GODZINA=0))
INTO :Z_ID, :IDMAG
DO BEGIN
FOR SELECT P.IDTOW,P.ILOSC,P.CZNETTO,P.CZNETTO,P.CSBRUTTO
FROM POZSPRZEDAZ P
WHERE P.IDSPR /*fk NOT NULL*/= Z.ID/*PK*/
/* tell me if this apply and/or helps taken from the having
clause*/
and P.ILOSC<>0 and P.CSNETTO<>0
/* - - - */
INTO :IDTOW,:ILOSC,:CZNETTO,:CZNETTO,:CSBRUTTO
DO BEGIN
SUSPEND;
END
END
END

CREATE PROCEDURE sp_X RETURNS
(
IDSPR BIGINT,
Z_ID BIGINT,
IDMAG BIGINT,
IDTOW BIGINT,
ILOSC DECIMAL(18,3),
CZNETTO DECIMAL(18,4),
CZNETTO DECIMAL(18,4),
CSBRUTTO DECIMAL(18,4)
)
AS
BEGIN
/*Natural scan (8mill records) :(*/
FOR SELECT P.IDSPR,P.IDTOW,P.ILOSC,P.CZNETTO,P.CZNETTO,P.CSBRUTTO
FROM POZSPRZEDAZ P
/* tell me if this apply and/or helps taken from the having
clause*/
where P.ILOSC <>0 and P.CSNETTO<>0
/* - - - */
INTO :IDSPR,:IDTOW,:ILOSC,:CZNETTO,:CZNETTO,:CSBRUTTO
DO BEGIN
/*PK scan*/
FOR SELECT Z.ID, Z.IDMAG
FROM SPRZEDAZ Z
WHERE Z.ID = :P_IDSPR AND
Z.DATASPRZEDAZY BETWEEN '2005-02-01' AND '2005-02-28'
AND
((Z.GODZINA BETWEEN 8 AND 22) OR Z.GODZINA=0))
INTO :Z_ID, :IDMAG
DO BEGIN
SUSPEND;
END
END
END

HTH

Juan Jose