Gerhard Wiesinger wrote:
I've the following data: datetime | val1 | val2 time1 | 4 | 40% time2 | 7 | 30% time3 | 12 | 20% ... I'd like to sum up the following: (7-4)*30% + (12-7)*20% + ... datetime is ordered (and unique and has also an id).
1.) Self join with one row shift?
Self-join only helps if the id comes from a gap-less sequence. Row numbers could be used if available, but they are not in 8.3. A possible way of solving this (when a procedural method is not wanted) is to lay out the dataset in temporary arrays that are repeated for every row you need to compute. That can be arranged in a self-contained sql query, like this:
select sum((av1[i]-av1[i-1])*av2[i]) from (select av1,av2,generate_series(2,array_upper(av1,1)) as i from (select array_accum(val1) as av1, array_accum(val2) as av2 from (select val1,val2 from TABLENAME order by datetime) s0 ) s1 ) s2 However, this would probably be too slow for a large dataset. Best regards, -- Daniel PostgreSQL-powered mail user agent and storage: http://www.manitou-mail.org -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
