"Paolo Saudin" <paolo@ecometer.it> writes:
> I have a problem with a query wich simple aggregate values. In the sample
> below I have two values, 1.3 and 1.4. Rounding their average with one
> decimals, should give 1.4.
You seem way overoptimistic about float4 values being exact. They are
not. The actual computation being done here is more like
regression=# select (1.3::real + 1.4::real) / 2 ;
?column?
------------------
1.34999990463257
(1 row)
If you want an exact sum with no roundoff error you should be storing
all your values as numeric (and taking the consequent speed and space
hit :-().
regards, tom lane