How to select the duplicate value if both are in the same interval

[patydsc]

Hi,

can anyone help me to figure this out.
Currently, i have this code:

select 
  t_stamp, 
  num 
from table
where num in 
   (select num from click_log 
    where t_stamp between '2010-07-21 12:00:00' 
    and '2010-07-21 13:00:00'
    group by num 
    having count(*) > 1)
order by num;

this code will get the duplicate values within interval of 1 hour. This is not the problem. the problem is how to get duplicate values for every 15 mins of time range (0-15,15-30,30-45,45-60) within interval of 1 hour.

lets say if my records look like this:

tstamp              | num
--------------------+-----
2010-07-21 11:59:05 |  a
2010-07-21 12:05:23 |  a
2010-07-21 12:08:47 |  c
2010-07-21 12:11:30 |  a
2010-07-21 12:18:11 |  a
2010-07-21 12:24:09 |  b
2010-07-21 12:33:41 |  a
2010-07-21 12:35:29 |  b
2010-07-21 12:39:09 |  b
2010-07-21 12:43:51 |  a
2010-07-21 12:45:17 |  a
2010-07-21 12:49:05 |  c
2010-07-21 12:56:00 |  c
2010-07-21 13:10:32 |  a

the output should be look like this:

tstamp              | num
--------------------+-----
2010-07-21 12:05:23 |  a    } in 0-15mins
2010-07-21 12:11:30 |  a    }
_________________________
2010-07-21 12:33:41 |  a    } in 30-45mins
2010-07-21 12:35:29 |  b    }
2010-07-21 12:39:09 |  b    }
2010-07-21 12:43:51 |  a    }
_________________________
2010-07-21 12:49:05 |  c    } in 45-60mins
2010-07-21 12:56:00 |  c    }

I appreciate any help.

thanks :)

[patydsc]

fyi, i'm using postgres 8.2 :)

[rski]

All ranges in one query? Can you use UNION clauses?