I am looking for a way to aggregate timestamped data on a half hour interval, not just by the hour or minute. Suppose I have a table composed of: Date | Time | Data -----------+----------+------ 1999-12-19 | 10:00:00 | 76 1999-12-19 | 10:15:00 | 72 1999-12-19 | 10:30:00 | 77 1999-12-19 | 10:45:00 | 71 1999-12-19 | 11:00:00 | 74 1999-12-19 | 11:15:00 | 78 I can aggregate by the hour without problem: SELECT Date, date_trunc('hour', Time) AS HOUR, SUM(Data) FROM Table GROUP BY Date, HOUR; What I would like to do though is aggregate by each half hour or maybe even 20 minutes. Does anyone know a good way to do this? Thanks in advance, -Lars