title: Aggregating postgresql rows by date
body: <p>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 a.m. then i have records:
  - from monday 9 a.m. to tuesday 8 a.m (grouped in one record)
  - from tuesday 9 a.m. to wednesday 8 a.m. (grouped in one record)
  and so on.
  Thanks, for any ideas.</p>