Re: strange query plan

Mario Weilguni writes:

> Now when I type:
> explain select min(id)from log;
> NOTICE:  QUERY PLAN:
>
> Aggregate  (cost=45702.20..45702.20 rows=1 width=4)
>   ->  Seq Scan on log  (cost=0.00..41978.36 rows=1489536 width=4)
>
> I don't understand why the index log_pkey is not used here. I guess it would
> be much cheaper to consult the index to get min(), max(), sum() and avg()
> instead of sequentially scanning ~500MB of data.

Since your query reads the entire "log" table, it is certainly better to
use a sequential scan in the case of sum() and avg().  A min() and max()
would theoretically not need to scan the entire table in the presence of
an index, but unfortunately this doesn't work yet.

--
Peter Eisentraut      peter_e@gmx.net       http://yi.org/peter-e/