Re: Optimizer bug??

Ismail Kizir wrote:
> Hi everybody,
>
> 1 .... EXPLAIN SELECT COUNT(*) AS c FROM articletbl WHERE
> ((mydate BETWEEN '2004-04-24' AND '2004-05-24' )
> )
>
> 2 .... EXPLAIN SELECT COUNT(*) AS c FROM articletbl WHERE
> ((mydate = '2004-04-24')
> )
>
> (I ran VACUUM ANALYZE before running those)
>
> mydate is an indexed date column.
> The optimizer optimizes the second query but, it doesn't optimize the first
> one and decides to make a "sequential scan".
> Is this a bug?
> Or may someone explain me the reason?
>
> Thanks in advance.
>
> Ismail Kizir

If 2004-04-24 to 2004-05-24 make up let's say 90% of your data
PostgreSQL will find out that it is cheaper to use a seq scan instead of
an index.

This is not a bug at all - this is normal and desired behaviour ...

Regards,

Hans

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