Обсуждение: Is this query possible in PostgreSQL ?

Hi All

While reading some SQL books i crossed on SUBSETS querry, but it seems
postgres dont understand them.

Is there another way to do this in postgres ?
if so, where i can read about it ?

SELECT * from some_table WHERE MOD(some_row, :n) = 0;

Thanks in advance

Ben-Nes Michael wrote:
> Hi All
>
> While reading some SQL books i crossed on SUBSETS querry, but it seems
> postgres dont understand them.
>
> Is there another way to do this in postgres ?
> if so, where i can read about it ?
>
> SELECT * from some_table WHERE MOD(some_row, :n) = 0;

So this allows you to get every Xth result, like every 3rd row.  Wow,
that is interesting.  We don't have a ROWNUM like Oracle has, but if we
did you could just use mod on that:

    ROWNUM % 3 = 0


You could use a cursor and fetch only every Xth row.  Not sure what else
I can suggest.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> SELECT * from some_table WHERE MOD(some_row, :n) = 0;

> So this allows you to get every Xth result, like every 3rd row.  Wow,
> that is interesting.

s/interesting/useless/.  Every third row in what ordering?  And don't
tell me about ORDER BY, because WHERE conditions are processed before
ORDER BY.

            regards, tom lane