Aggregating postgresql rows by date

Question

I have records with values like: date, hour, value. Aggregating whole day is easy, i just group by date. My problem is that i need to aggregate records from whole days with specific start/end time. In example when start time is 9 am then i have records: - from monday 9 am to tuesday 8 am (grouped in one record) - from tuesday 9 am to wednesday 8 am (grouped in one record) and so on. Thanks, for any ideas.

Answer 1

I'm going to assume your hour field is an INT, but regardless you should be able to adapt this...

GROUP BY
  CASE WHEN hour >= 9 THEN date ELSE date - 1 END

This essentially treats any hour before 9am as being part of the previous day.

Answer 2

GROUP BY date_trunc('day',date+(hour-9)*interval '1h')或类似的东西？