I searched the messages but I didn't get a message related to my case,
so I figured I should post.

lets simplify the example and say :

table X
column A double precision
column B double precision
column F smallint

if I do:
select sum(a)/sum(b) from X no problem, everything is OK

If I do:

select
case when flag=1 then sum(a) else 0 end as SUM_A,
case when flag=1 then sum(B) else 0 end as SUM_B,
F
from X
group by F

again no problem, everything is OK

now, what I want to do is the following:
divide SUM_A/SUM_B, the two pseudo columns of the above example

in other words

select
sum(SUM_A)/sum(SUM_B) as SUMX,
F
from
( select
case when flag=1 then sum(a) else 0 end as SUM_A,
case when flag=1 then sum(B) else 0 end as SUM_B,
F
from X
group by F)
group by F

I get the 'arithmetic exception, numeric overflow, or string truncation'
strange thing is that multiplication

select sum(SUM_A) * sum(SUM_B) as SUMX,

works alright.
Also if I try to divide straight double precision numbers like
"12345.12345 / 12345.12345 as as SUMX", again no problem.

I tried lots of workarounds such as casting the pseudo columns in
other datatypes to no avail.

also i tried to fool firebird and instead of sum(SUM_A)/sum(SUM_B) as
SUMX, i did sum(SUM_A) * (1/sum(SUM_B)) as SUMX, but again I failed.

I'm certain that no division by zero occurs, even if i reverse the
order i.e. sum(SUM_B)/sum(SUM_A) as SUMX, I still get the error.

Anyone has come across anything like this? any help will be greatly
appreciated, thanks in advance.