Re: returning row numbers in select

>> I to return a sequential row number beginning at 1?
>>
>> i.e.
>>
>> row|         timestamp
>> ---+----------------------------
>> 1   2004-02-01 23:15:00.824-05
>> 2   2004-02-01 23:15:01.824-05
>> 3   2004-02-01 23:15:02.824-05
>> ...
>>
>> My reason for wanting row numbers is so I can use a 'MOD(row_number,
>> n)' to get the nth row from the table.

Correction, I don't want to simply get the nth row, I want all rows
that are divisible by n.  Essentially, the timestamp is at a regular
interval and I want a way of selecting rows at different sampling
intervals.

> Doesn't LIMIT and OFFSET do the job?
> http://www.postgresql.org/docs/7.3/interactive/queries-limit.html

It would if I only wanted an offset butI want a query to return the
first, fifth, and tenth, and so on row.  This would be 'MOD(row_num,
5)' but given that I don't know the number of rows a priori, it is
difficult to write a LIMIT.  Moreover, the offset doesn't make it easy
to get the first row.  Unless, of course, I am missing something
obvious?

Cheers,
Randall