Re: transposed query?

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
>
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>

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