Re: date_trunc to aggregate values?

2013/2/4 Kirk Wythers <wythe001(at)umn(dot)edu>:
> I am looking for suggestions on aggregation techniques using a timestamp column. In my case I have tried:
>
> date_trunc('hour', derived_tsoil_fifteen_min_stacked.time2),
>
> but date_truck only seems to aggregate the timestamp. I thought I could use
>
> AVG(derived_tsoil_fifteen_min_stacked.value)
>
> in combination with date_trunk, but I still get 15 minute values, not the hourly average from the four 15 minute records.
>
> rowid date_truck time2 site canopy plot variable name value avg
> 2010-07-07_00:00:00_b4warm_a 2010-07-07 00:00:00 1 2010-07-07 00:00:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 21.06 21.0599994659424
> 2010-07-07_00:15:00_b4warm_a 2010-07-07 00:00:00 1 2010-07-07 00:15:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.96 20.9599990844727
> 2010-07-07_00:30:00_b4warm_a 2010-07-07 00:00:00 1 2010-07-07 00:30:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.88 20.8799991607666
> 2010-07-07_00:45:00_b4warm_a 2010-07-07 00:00:00 1 2010-07-07 00:45:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.8 20.7999992370605
> 2010-07-07_01:00:00_b4warm_a 2010-07-07 01:00:00 1 2010-07-07 01:00:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.72 20.7199993133545
> 2010-07-07_01:15:00_b4warm_a 2010-07-07 01:00:00 1 2010-07-07 01:15:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.64 20.6399993896484
> 2010-07-07_01:30:00_b4warm_a 2010-07-07 01:00:00 1 2010-07-07 01:30:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.55 20.5499992370605
> 2010-07-07_01:45:00_b4warm_a 2010-07-07 01:00:00 1 2010-07-07 01:45:00 cfc closed a2 tsoil_sc tsoil_avg1_sc 20.47 20.4699993133545
>
> I was tying to get two records out of this set, with the 'avg" column representing the mean of the first and last four of each 15 minute records.
>
> Suggestions?

Are you using an explicit GROUP BY?

--
Jason Dusek
pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B