Re: Analytic type functionality, matching patters in a column then increment an integer - Mailing list pgsql-general

On 05/10/11 19:29, Henry Drexler wrote:
>
> and would like to have a column indicate like this:
>
> 'evaluation' 'indicator'
> tf                     1
> tt                     1
> ft                      1
> ff
> ff
> tf                      2
> ft                      2
> tf                      3
> tt                      3
> ft                      3
> ff

SELECT id,evaluation,sum(case when evaluation='tf' then 1 else 0 end)
over (order by id) FROM tfcount ORDER BY id;

id | evaluation | sum
----+------------+-----
   1 | tf         |   1
   2 | tt         |   1
   3 | ft         |   1
   4 | ff         |   1
   5 | ff         |   1
   6 | tf         |   2
   7 | ft         |   2
   8 | tf         |   3
   9 | tt         |   3
  10 | ft         |   3
  11 | ff         |   3
(11 rows)

OK, so that's almost it, but you'd like "ff" to be null. You probably
can do it with a suitably nested CASE, but it's probably clearer as a
sub-query.

SELECT
   id,
   evaluation,
   CASE WHEN evaluation='ff' THEN null::int
   ELSE sum::int END AS section_num
FROM (
   SELECT
     id,
     evaluation,
     sum(case when evaluation='tf' then 1 else 0 end) over (order by id)
   FROM tfcount
) AS rows
ORDER BY id;

HTH

P.S. - I always find the windowing function syntax confusing, but it's
as the standards define I believe.

--
   Richard Huxton
   Archonet Ltd