Re: transposed query? - Mailing list pgsql-general

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