Re: partial time stamp query

Select time2::date, extract('hour' from time2), AVG(avg) from tablename
group by time2::date, extract('hour' from time2)

On Monday, February 4, 2013, Kirk Wythers wrote:

> Hi Brent,
>
> Nice to hear from you. I hope your world is good.
>
> On Feb 4, 2013, at 2:14 PM, Brent Wood <Brent(dot)Wood(at)niwa(dot)co(dot)nz<javascript:;>>
> wrote:
>
> > Hi Kirk,
> >
> > We have a (near) real time data database for instrument observations
> from our research vessels. All observations (summarised to one minute
> intervals - the actual raw data is in netCDF, this database makes for
> easier access & meets most users needs) go into a single table, with other
> tables for metadata about platforms, instruments, etc. Now approaching 350m
> records, so reasonably substantial.
> >
> > Underlying optimisations include
> >
> > partitioned readings table, with a separate partition for each year (now
> 23 years)
> > clustered index on timestamp for the previous years partitions.
> > largeish filesystem block size - tested to work well with the clustered
> index & small size records)
> >
> > These generally make a big difference to performance. To address one
> issue, much like yours, where some users want hourly data for a year, some
> want daily data for 10 years & some want 1 minute data for the last month
> (& some, no doubt, want one minute data for 20+ years!) I introduced an
> integer column called timer. This value is set according to the time (not
> date) of each record.
>
> Very similar to what I need to do. Our main table consists of records that
> have been standardized to 15 minute timestamps. Here is a simplified example
>
> record timestamp variable value
> 1 12:00:00 temp 12.6
> 2 12:15:00 temp 12.3
> 3 12:30:00 temp 11.7
> 4 12:45:00 temp 12.3
> 5 13:00:00 temp 13.9
> 6 13:15:00 temp 12.5
> 7 13.30:00 temp 13.7
> 8 13:45:00 temp 12.0
>
> You are exactly right, some people will want the original 15 minute
> version, some people will want these summarized to hourly data, and others
> will want these summarized to daily data. Still others may be satisfied
> with monthly summaries.
>
> >
> > Along the lines of (from memory) :an even no of minutes after the hour
> is 2, 5 minutes is 4, 10 minutes is 8, 15 minute is 16, 30 minutes is 32,
> 60 minutes is 64, 6 hourly is 128, 12:00 AM is 256 & 12:00PM is 512. When
> any timestamp is in more than one category (eg: 12:00 is all of even, 5,
> 15m 30m 60 minutes), the timer value is set to the largest appropriate one.
>
> I'm not quite following. In my case, if I want hourly data, I'd be looking
> for…
>
> record timestamp variable value
> 1 12:00:00 temp 12.225
> 2 13:00:00 temp 13.025
>
> Are you saying that I could use an approach that WHILE statement?
> Something like:
>
> WHILE data_truc('hour', timestamp) = 12:00:00, then calulate AVG(value)?
>
> >
> > So a request for:
> > 1 minute data is select from table;
> > 2 minute data is select from table where timer >=2 and timer !=15 and
> timer !=4;
> > hourly data is select from table where timer >=64 and timer != 15 and
> timer != 4;
> > etc
> >
> > 5 & 15 minute add a bit of complexity, but we gave the users what they
> wanted. This has worked well for years now, & we have an internal web
> (mapserver/openlayers based) application allowing users to visualise &
> download their selected data - they choose from an interval pick list & the
> SQL is hidden. Some extra enhancements are the automatic collation of lat &
> lon gps readings into a Postgis point for each reading record, & the
> automatic aggregation of daily points into daily track lines, so the track
> for any selected set of dates can easily be displayed on a map (the
> platforms are mobile vessels - not fixed sites)
> >
> > You might adapt some of these ideas for your use case?
> >
> > Cheers
> >
> > Brent Wood
> >
> > Programme leader: Environmental Information Delivery
> > NIWA
> > DDI: +64 (4) 3860529
> > ________________________________________
> > From: pgsql-general-owner(at)postgresql(dot)org [
> pgsql-general-owner(at)postgresql(dot)org] on behalf of Kirk Wythers [
> wythe001(at)umn(dot)edu]
> > Sent: Tuesday, February 05, 2013 5:58 AM
> > To: pgsql-general(at)postgresql(dot)org
> > Subject: Fwd: [GENERAL] partial time stamp query
> >
> > Thanks. That worked great! Now I am trying to aggregate these same
> fifteen minute to hourly. I have tried using date_trunk:
> >
> > date_trunc('hour', derived_tsoil_fifteen_min_stacked.time2),
> >
> > but date_truck only seems to aggriage 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.
> >
> > Perhaps date_trunk only works for the timestamp?
> >
> >
> >
> > On Feb 4, 2013, at 8:50 AM, Misa Simic <misa(dot)simic(at)gmail(dot)com<mailto:
> misa(dot)simic(at)gmail(dot)com>> wrote:
> >
> > WHERE derived_tsoil_fifteen_min_stacked.time2::date = '2010-07-07'::date
> >
> > On Monday, February 4, 2013, Kirk Wythers wrote:
> > I am trying to write a query that grabs one particular day from a
> timestamp column. The data are ordered in 15 minute chunks like this:
> >
> > 2010-07-07 12:45:00
> > 2010-07-07 13:00:00
> > 2010-07-07 13:15:00
> > 2010-07-07 13:30:00
> > etc…
> >
> > If I wanted all records from july 7th 2010, I would expect 4 x 24 = 96
> records per day.
> >
> > I have tried the '=' operator, like this
> >
> > WHERE derived_tsoil_fifteen_min_stacked.time2 = '2010-07-07*'
> >
> > but that grabs nothing, and using the '~' operator grabs everything with
> a 2010 or 07 in it… in other word