Re: How to fetch values at regular hours?

[Goran Hasse <gorhas@xxxxxxxxx>]

Yes timestamp and count - is not good names for columns...

I tried something like;


select name,date_trunc('hour',timestamp),timestamp,count from counter_log_view where name='CNT-3' and timestamp < '2010-05-23 20:00:00'  order by timestamp limit 10;
 name  |     date_trunc      |         timestamp          | count 
-------+---------------------+----------------------------+-------
 CNT-3 | 2010-05-23 15:00:00 | 2010-05-23 15:43:17.411386 |    23
 CNT-3 | 2010-05-23 15:00:00 | 2010-05-23 15:53:17.45934  |    24
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:03:17.489321 |    24
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:13:17.586089 |    24
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:23:17.69116  |    25
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:33:17.795955 |    28
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:43:17.89265  |    28
 CNT-3 | 2010-05-23 16:00:00 | 2010-05-23 16:53:17.989268 |    30
 CNT-3 | 2010-05-23 17:00:00 | 2010-05-23 17:03:18.1447   |    33
 CNT-3 | 2010-05-23 17:00:00 | 2010-05-23 17:13:18.199568 |    35
(10 rader)

Seems promising... But then I would like to select only the last from date_trunc...

Hm...

GH

2010/5/25 Tim Landscheidt <tim@xxxxxxxxxxxxxxxxxx>

Goran Hasse <gorhas@xxxxxxxxx> 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 :-).

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