Thank you all for your replies.
So, is there any precise way to discover when sorting is invoked?
Thanks.
Regards.
Fava
Il 11/02/2011 01:17, Robert Haas ha scritto:
> On Thu, Feb 10, 2011 at 6:21 PM, Nicolas Barbier
> <nicolas.barbier@gmail.com> wrote:
>> 2011/2/10 mac_man2008@yahoo.it<mac_man2008@yahoo.it>:
>>
>>> Which operations invoke the sorting algorithms implemented in the sorting
>>> module (tuplesort.c) ?
>>> Of course, one of those operations invoking sorting is the ORDER BY clause
>>> and the DISTINCT too.
>>>
>>> Moreover, the Merge Join should be implemented invoking sorting.
>>>
>>> Is there any other operation invoking sorting?
>> AFAIK, all set operators except for UNION ALL. (I am probably missing
>> a whole boatload of other things.)
> Merge joins don't necessarily involve a sort - you could do a merge
> over a pair of index scans, for example.
>
> Set operations can be implemented using hashing or sorting, too.
>