I've had this issue for long time and I haven't found a better
solution than to seperate it in several statements in a SP like this:

FOR Select ...
From P INNER JOIN Z
group by...
into :...
do begin
FOR SELECT ...
from T
where PK = :...
into :...;

FOR SELECT ...
from M
where PK = :...
into :...;

suspend;
end

I suppose that all the result set is defined by "P INNER JOIN Z" the
others are only "useful fields". So you go into T and M only the
minimal necessary times.

I've been evaluating FB2. and I know this issuse is going to be
solved by using derived tables and by using the execute block
statement. I already tested and works fine, just as S.P.

Anyways I still think that the optimizer should detect this scenario
and "optimeze" for it.

---

other approach:

> P: 590210 out of 8 mill
> Z: 339244 out of 4 mill
> T: 590210
> M: 334822

How many records and reads do you get when you do a:
SELECT 1
FROM Z
WHERE
DATASPRZEDAZY BETWEEN '2005-02-01' AND '2005-2-28' AND
((Z.GODZINA BETWEEN 8 AND 22) OR Z.GODZINA=0))

Depending on the results, you could separate P from Z.

ok!
I hope this help, and that this kind of tune won't be necessary in
future versions of FB.

Juan Jose.