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Given f1(x) as IMMUTABLE and f2(x) as IMMUTABLE, and f3(f1,f2) as
IMMUTABLE, does the query planner cache the result of f3 and reuse it
or if you want to get a little more speed you better explicitly define
yourself f3 as IMMUTABLE?
I had an aggregate query like:
select id, sum(p1*f1(a)/f2(b) as r1, sum(p2*f1(a)/f2(b) as r2, ... sum(pn*f1(a)/f2(b) as rn
...
group by id;
Where f1(x) and f2(x) were defined as IMMUTABLE.
By the experiments I ran looks like after defining a new function
f3(a,b):= f1(a)/f2(b) and rewriting the query as:
select id, sum(p1*f3(a,b) as r1, sum(p2*f3(a,b) as r2, ... sum(pn*f3(a,b) as rn
...
group by id;
*Looks like* I got a little (5%) improvement in performance of the
query. Is there a way to find out if the function is re-evaluated each
time?
Is this the recommended way to proceed?
Thank you!
Petru Ghita
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