Re: How to fetch values at regular hours?

Goran Hasse <gorhas(at)gmail(dot)com> wrote:

> [...]
> I would like to do;

> freescada=> select * from counter_log_view where name='CNT-3' and timestamp
> < '2010-05-23 18:00:00' order by timestamp desc limit 1;
> name | timestamp | count
> -------+---------------------------+-------
> CNT-3 | 2010-05-23 17:53:18.58674 | 43
> (1 rad)

> freescada=> select * from counter_log_view where name='CNT-3' and timestamp
> < '2010-05-23 19:00:00' order by timestamp desc limit 1;
> name | timestamp | count
> -------+----------------------------+-------
> CNT-3 | 2010-05-23 18:53:19.151988 | 50
> (1 rad)

> freescada=> select * from counter_log_view where name='CNT-3' and timestamp
> < '2010-05-23 20:00:00' order by timestamp desc limit 1;
> name | timestamp | count
> -------+----------------------------+-------
> CNT-3 | 2010-05-23 19:53:19.683514 | 51
> (1 rad)

> In one query. Is this possible in *any* way?

Sure:

| SELECT DISTINCT ON (DATE_TRUNC('hour', timestamp)) name, timestamp, count
| FROM counter_log_view
| ORDER BY DATE_TRUNC('hour', timestamp), timestamp DESC;

Tim

P. S.: Naming columns "timestamp" and "count" will lead to
trouble :-).