Re: transposed query?

Nick Barr wrote:

> javier garcia - CEBAS wrote:
>
>> Hi;
>> I've got problems with a query. I'm not sure if it is possible to do
>> this with Postgres, although I think it should be.
>>
>> I had resolved these kind of queryes in MSAccess, where they are
>> called "cross references querys" but I can't find my way in Postgres.
>>
>> My table 'muestras_rambla' is like:
>> date | id_punto | muestra | flow | n_nitrato ...
>> --------------------------+----------+---------+---------+-----------
>> 06/02/2003 00:00:00 CET | 1 | 1 | 699.462 | 18.44
>> 06/02/2003 00:00:00 CET | 1 | 2 | 699.462 | 13.79
>> 06/02/2003 00:00:00 CET | 2 | 1 | 341.05 | 11.15
>> 06/02/2003 00:00:00 CET | 2 | 2 | 341.05 | 17.3
>> 06/02/2003 00:00:00 CET | 3 | 1 | 514.05 | 22.17
>> 06/02/2003 00:00:00 CET | 3 | 2 | 514.05 | 16.62
>> 06/02/2003 00:00:00 CET | 4 | 1 | 466.884 | 18.99
>> 06/02/2003 00:00:00 CET | 4 | 2 | 466.884 | 19.02
>> 06/02/2003 00:00:00 CET | 6 | 1 | 30.012 | 5.91
>> 06/02/2003 00:00:00 CET | 6 | 2 | 30.012 | 4.15
>> 19/02/2003 00:00:00 CET | 1 | 1 | 911.43 | 17.66
>> 19/02/2003 00:00:00 CET | 1 | 2 | 911.43 | 9.23
>> ...
>>
>> where I 'id_punto' can take the values from 1 to 6, and muestra is 1
>> or 2. Commonly, for each 'date' and 'id_punto' we have two samples
>> (muestra), and the 'flow' is also commonly the same for the two samples.
>>
>> The case is that for every 'date' I want to have the 'time series' of
>> flows in the way:
>> date 1 2 3 4 6
>> 03/10/2002 606.92 323.08 440.69 393.61 5.49
>> 17/10/2002 348.19 400.32 319.33 211.26 2.53
>> 29/10/2002 411.57 409.66 310.37 362.20 9.36
>> 14/11/2002 446.96 373.72 302.79 348.69 5.18
>> 26/11/2002 381.20 386.85 307.77 240.75 6.41
>> 12/12/2002 416.84 307.03 317.94 249.36 5.64
>> 26/12/2002 743.04 380.30 539.94 521.60 3.69
>> 09/01/2003 403.07 301.16 370.30 379.41 3.69
>> ...
>>
>> where the names of the rows are the values in 'id_punto' and the
>> values of the data are the average (for every 'id_punto' and 'date')
>> between the two samples (muestra).
>>
>> In MSaccess this is solve with:
>> TRANSFORM avg(muestras_rambla.flow) AS avg_flow
>> SELECT muestras_rambla.date
>> FROM muestras_rambla
>> GROUP BY muestras_rambla.date
>> PIVOT muestras_rambla.id_punto;
>>
>> All I can do in postgres is :
>> --------
>> SELECT muestras_rambla.fecha, id_punto, avg(caudal) AS avg_caudal
>> FROM muestras_rambla
>> GROUP BY fecha, id_punto
>> --------
>> to get:
>> fecha | id_punto | avg_caudal
>> --------------------------+----------+------------------
>> 03/10/2002 00:00:00 CEST | 1 | 606.924
>> 03/10/2002 00:00:00 CEST | 2 | 323.079
>> 03/10/2002 00:00:00 CEST | 3 | 440.690
>> ...
>> But, how could manage this to get the 'time series' table?
>>
>> Thanks for your help and best wishes
>>
>> Javier
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 5: Have you checked our extensive FAQ?
>>
>> http://www.postgresql.org/docs/faqs/FAQ.html
>>
>
> How about:
>
>
> SELECT
> date,
> (SELECT s1.flow FROM muestras_rambla s1 WHERE s1.date=t1.date AND
> s1.id_punto=1) AS flow_1,
> (SELECT s2.flow FROM muestras_rambla s2 WHERE s2.date=t1.date AND
> s1.id_punto=2) AS flow_2,
> (SELECT s3.flow FROM muestras_rambla s3 WHERE s3.date=t1.date AND
> s1.id_punto=3) AS flow_3,
> (SELECT s4.flow FROM muestras_rambla s4 WHERE s4.date=t1.date AND
> s1.id_punto=4) AS flow_4,
> (SELECT s6.flow FROM muestras_rambla s6 WHERE s6.date=t1.date AND
> s1.id_punto=6) AS flow_6
> FROM
> muestras_rambla t1
> GROUP BY
> t1.date;
>
>
> This uses sub-queries in the Select clause to get the data in columns.
> There may be another way.
>
>
>
> Nick Barr
>

Ooops, having tested that query I found a typo (or four). Try:

SELECT
date,
(SELECT s1.flow FROM muestras_rambla s1 WHERE s1.date=t1.date AND
s1.id_punto=1) AS flow_1,
(SELECT s2.flow FROM muestras_rambla s2 WHERE s2.date=t1.date AND
s2.id_punto=2) AS flow_2,
(SELECT s3.flow FROM muestras_rambla s3 WHERE s3.date=t1.date AND
s3.id_punto=3) AS flow_3,
(SELECT s4.flow FROM muestras_rambla s4 WHERE s4.date=t1.date AND
s4.id_punto=4) AS flow_4,
(SELECT s6.flow FROM muestras_rambla s6 WHERE s6.date=t1.date AND
s6.id_punto=6) AS flow_6
FROM
muestras_rambla t1
GROUP BY
t1.date;

Nick Barr