Re: "select c1, method(c2) group by c1" returns all values of c2 for c1

2011/2/8 Emi Lu <emilu@encs.concordia.ca>:
> On 02/08/2011 02:51 PM, Rolando Edwards wrote:
>>
>> SELECT distinct c1,array_to_string(array(SELECT c2 FROM T1 B where
>> A.c1=B.c1),', ') from T1 A order by c1;
>>
>> Give it a Try !!!
>
>
> Thanks a lot! Very helpful!
>
> array_to_string() + array() is exactly what I am looking for!
>
> I just wonder that array_to_string() + array() will provide me good
> performance, right? If the calculation will be based on millions records.

it depend on number of groups. This is correlated subquery - it must
not be a best.

Regards

Pavel Stehule

the best speed gives a string_agg, but it is only in 9.0



>
> Thanks again!
> --
> Lu Ying
>
>
>
>
>
>> Rolando A. Edwards
>> MySQL DBA (SCMDBA)
>>
>> 155 Avenue of the Americas, Fifth Floor
>> New York, NY 10013
>> 212-625-5307 (Work)
>> 201-660-3221 (Cell)
>> AIM&  Skype : RolandoLogicWorx
>> redwards@logicworks.net
>> http://www.linkedin.com/in/rolandoedwards
>>
>>
>> -----Original Message-----
>> From: pgsql-sql-owner@postgresql.org
>> [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of Emi Lu
>> Sent: Tuesday, February 08, 2011 2:36 PM
>> To: pgsql-sql@postgresql.org
>> Subject: [SQL] "select c1, method(c2) group by c1" returns all values of
>> c2 for c1
>>
>> Good afternoon,
>>
>> Is there a method to retrieve the following results:
>>
>> T1(c1 int, c2 varchar(128) )
>> ---------------------------------
>>
>>
>> (1, val1);
>> (1, val2);
>> (1, val3);
>> (2, val1);
>> (3, val5);
>> (3, val6);
>>
>> select c1, method(c2)
>> group by c1
>>
>> returns:
>> ============
>> 1,   "val1, val2, val3"
>> 2,   "val1"
>> 3,   "val5, val6"
>>
>>
>> Thanks a lot!
>>
>> --
>> Lu Ying
>>
>
>
> --
> Emi Lu, ENCS, Concordia University, Montreal H3G 1M8
> emilu@encs.concordia.ca        +1 514 848-2424 x5884
>
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