Re: date_trunc to aggregate values?

On Feb 4, 2013, at 3:26 PM, Jason Dusek <jason(dot)dusek(at)gmail(dot)com> wrote:

> 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?
>

Here is what I have in the GROUP BY clause

GROUP BY
date_trunc('hour', derived_tsoil_fifteen_min_stacked.time2),
derived_tsoil_fifteen_min_stacked.time2,
data_key.site,
data_key.canopy,
data_key.variable_name,
data_key.plot