Re: Help with select with max and min please - Mailing list pgsql-general

On 08/08/10 20.47, Jose Maria Terry wrote:
> Hello all,
>
> I need to run a query on a table that holds logged data from several
> water flow meters.
>
> I need the first and last values (with their associated time) for every
> logger in a time range.
>
> I've tried this that returns the min and max time in the desired range
> for every logger, but i don't know how to get the associated data (the
> row called caudal) for min and max .
>
> select remota_id,min(hora),max(hora) from historicos where hora >
> '2010-08-07' and hora <'2010-08-08 00:03' group by remota_id order by
> remota_id;
>
> remota_id | min | max
> -----------+---------------------+---------------------
> 01 | 2010-08-07 00:00:30 | 2010-08-08 00:00:30
> 02 | 2010-08-07 00:00:06 | 2010-08-08 00:00:06
> 03 | 2010-08-07 00:00:03 | 2010-08-08 00:00:02
> 04 | 2010-08-07 00:00:06 | 2010-08-08 00:00:06
> 05 | 2010-08-07 00:00:01 | 2010-08-08 00:00:02
> 06 | 2010-08-07 00:00:02 | 2010-08-08 00:00:02
> 07 | 2010-08-07 00:00:06 | 2010-08-08 00:00:06
> 09 | 2010-08-07 00:00:06 | 2010-08-08 00:00:06
> (8 filas)
>
> I need some like this:
>
> remota_id | min | max | min_caudal | max_caudal
> -----------+---------------------+---------------------+------------+------------
>
> 01 | 2010-08-07 00:00:30 | 2010-08-08 00:00:30 | 976.04 | 904.21
> 02 | 2010-08-07 00:00:06 | 2010-08-08 00:00:06 | 829.71 | 764.42
>
> Where min_caudal is the value of caudal in hora = min() and max_caudal
> is the same for hora=max()

this can help?
select remota_id,min(hora),max(hora), (SELECT caudal FROM historicos
WHERE remota_id=ooo.remota_id AND hora=min(ooo.hora)) as min_caudal,
(SELECT caudal FROM historicos WHERE remota_id=ooo.remota_id AND
hora=max(ooo.hora)) as max_caudal from historicos AS ooo group by
remota_id order by remota_id;

Edoardo

>
> The data in the table is like this:
>
> select hora,remota_id,caudal from historicos;
>
> hora | remota_id | caudal
> ---------------------+-----------+----------
> 2010-05-21 20:00:06 | 04 | 1201.309
> 2010-05-21 20:15:08 | 04 | 1201.309
> 2010-05-21 20:30:06 | 04 | 1219.803
> 2010-05-21 20:45:06 | 04 | 1225.098
> 2010-05-21 21:00:06 | 04 | 1238.359
> 2010-05-21 21:15:06 | 04 | 1241.015
> 2010-05-21 21:30:06 | 04 | 1241.015
> 2010-05-21 21:45:06 | 04 | 1246.33
> 2010-05-21 22:00:06 | 04 | 1248.989
> 2010-05-21 22:15:06 | 04 | 1235.704
> 2010-05-21 22:30:06 | 04 | 1222.45
> 2010-05-21 22:45:06 | 04 | 1201.309
> 2010-05-21 23:00:06 | 04 | 1203.947
> 2010-05-21 23:15:06 | 04 | 1219.803
> 2010-05-21 23:30:06 | 04 | 1275.649
> 2010-05-21 23:45:06 | 04 | 1280.995
> 2010-05-22 00:00:06 | 04 | 1294.38
> 2010-05-22 00:15:06 | 04 | 1299.742
> 2010-05-22 00:30:06 | 04 | 1294.38
> 2010-05-22 00:45:06 | 04 | 1294.38
> 2010-05-22 01:00:06 | 04 | 1299.742
>
> Can anyone help me?
>
> Best,
>
>
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