On Sun, Mar 25, 2018 at 12:00 AM, Laurenz Albe wrote:
> Peter wrote:
>> Given an arbitrary function fn(x) returning numeric.
>>
>> Question: how often is the function executed?
>> [...]
>> C.
>> select v.v,v.v from (select fn('const') as v) as v;
>>
>> Answer:
>> Once if declared VOLATILE.
>> Twic
On 25 March 2018 at 18:00, Laurenz Albe wrote:
> Peter wrote:
>> Over all, VOLATILE performs better than STABLE.
>
> The reason is that the subquery with the VOLATILE function can be
> flattened; see the EXPLAIN (VERBOSE) output.
>
> There is not guarantee that less volatility means better perform
Peter wrote:
> Given an arbitrary function fn(x) returning numeric.
>
> Question: how often is the function executed?
> [...]
> C.
> select v.v,v.v from (select fn('const') as v) as v;
>
> Answer:
> Once if declared VOLATILE.
> Twice if declared STABLE.
>
> Now this IS a surprize. It is clear th
Given an arbitrary function fn(x) returning numeric.
Question: how often is the function executed?
A.
select fn('const'), fn('const');
Answer:
Twice.
This is not a surprize.
B.
select v,v from fn('const') as v; [1]
Answer:
Once.
C.
select v.v,v.v from (select fn('const') as v) as v;
