Re: Sorting. When?

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.

-- 
Robert Haas
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