Re: Performance question

On Mon, 10 Sep 2001, Tille, Andreas wrote:

> On Mon, 10 Sep 2001 Herbert(dot)Liechti(at)thinx(dot)ch wrote:
>
> > Use explain. Explain tells you the query plan of the optimizer.
> >
> > explain SELECT .....;
> Thanks I just found the thread "Index usage question" and tried to make
> some profit from it:
>
> explain SELECT Hauptdaten_Fall.MeldeKategorie, Count(Hauptdaten_Fall.ID) AS Anz FROM Hauptdaten_Fall WHERE (((Hauptdaten_Fall.IstAktuell)=20)) GROUP BY Hauptdaten_Fall.MeldeKategorie ORDER BY Hauptdaten_Fall.MeldeKategorie;
>
> NOTICE: QUERY PLAN:
>
> Aggregate (cost=35267.33..36154.62 rows=17746 width=16)
> -> Group (cost=35267.33..35710.98 rows=177458 width=16)
> -> Sort (cost=35267.33..35267.33 rows=177458 width=16)
> -> Seq Scan on hauptdaten_fall (cost=0.00..15024.12 rows=177458 width=16)

I assume that an index on the field IstAktuell avoids the sequential scan.
If an index is there try the following statement before you submit the
query:

set enable_seqscan = off;

Regards Herbie
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Herbert Liechti http://www.thinx.ch
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