Re: Incomprehensible dogged sort in Merge Join

Gregory Stark wrote:
> "Aleksandr Vinokurov" <aleksandr(dot)vin(at)gmail(dot)com> writes:
>
>> And that is its plan (attached one is the same, but with costs):
>>
>>> ---------------------------------<cut>--------------------------------<
>> Merge Left Join
>> Merge Cond: ("outer".name = "inner".name)
>> -> Sort
>> Sort Key: log.name
>> -> Seq Scan on log_example_3 log
>> -> Sort
>> Sort Key: uh.name
>> -> Subquery Scan uh
>> -> Sort
>> Sort Key: name
>> -> Seq Scan on user_history
>>> ---------------------------------<cut>--------------------------------<
>
> What version are you running with?

8.0.1, sorry for missing.

>
> Incidentally with CVS HEAD I see it working:
>
> postgres=# explain select * from (select * from a order by i) as a right join b on a.i = b.i ;
> QUERY PLAN
> -----------------------------------------------------------------
> Merge Right Join (cost=299.56..675.13 rows=22898 width=16)
> Merge Cond: (public.a.i = b.i)
> -> Sort (cost=149.78..155.13 rows=2140 width=8)
> Sort Key: public.a.i
> -> Seq Scan on a (cost=0.00..31.40 rows=2140 width=8)
> -> Sort (cost=149.78..155.13 rows=2140 width=8)
> Sort Key: b.i
> -> Seq Scan on b (cost=0.00..31.40 rows=2140 width=8)
> (8 rows)
>
>
>
>> With best regards to all of you,
>> Aleksandr.
>> ÿþ
>
> gesundheit.
>
>

Best wishes,
Aleksandr.