Merlin Moncure-2 wrote > On Tue, Mar 4, 2014 at 1:49 PM, Owen Hartnett <
> owen@ > > wrote: > >> It looks like I should be able to use the window function to do this, >> but >> I've been unsuccessful. The following runs, but doesn't seem to have any >> effect: >> >> select owner_id, array_agg(trim(maplot)), array_agg(revallandvalue + >> revalbuildingvalues) from parcel group by owner_id >> window mywindow as (rows between current row and 5 following); >> >> Does anyone have any suggestions on what I should try? >> >> -Owen > > I didn't test it, but something along the lines of: > > select > owner_id, > array_agg(maplot), > array_agg(totalvalues) > from > ( > select > owner_id, > trim(maplot) as maplot, > revallandvalue + revalbuildingvalues as totalvalues, > row_number() over (partition by owner_id) as n > from parcel > ) q > group by owner_id, (n - 1)/5; Yeah, a window cannot work because it cannot be defined to provide disjoint subsets. In most cases multiple invocations of array_agg(...) - at the same level in a query - will see the same row order but that is not something that it is wise to rely upon. Any time you want to have synchronized array_agg(...) calls you should add identical explicit ORDER BY clauses to them; or better yet combine that data into a custom datatype and then store that in the array. The solution is as Merlin presents; you need to use integer division to bucket the rows and then call the array_agg(...) using those groups. I like to keep the bucket ID around in order to capture the original order but as shown it is not a requirement. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/SQL-question-on-chunking-aggregates-tp5794680p5794694.html Sent from the PostgreSQL - general mailing list archive at Nabble.com. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
