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Oleg
On Fri, 7 Oct 2005, han.holl@informationslogik.nl wrote:
>
> Hello,
>
> We have a table of people with a date-of-birth and a surname, both indexed.
> We have queries like this:
> select report from table where dateofbirth = '1966-12-12' and surname like
> 'boer%'
>
> The planner estimates that in a 1.5M record table 'boer%' will have one record
> and 1966-12-12 about 40.
> Unfortunately, names are not evenly distributed, and in some combinations it
> will have to process many thousands of records. On some older and slower
> systems, this hurts.
>
> Is there a way to tell the planner to always prefer the dateofbirth index ?
> Alternatively, to inform it about the wildly uneven distribution of surnames
> (this must be even worse in China).
>
> A third possibility would be to rewrite such a query as a nested query: is
> there a rewrite query - hook (like apaches mod_rewrite) available ? Or is
> there a somewhere a proxy-server that could do this ?
>
> Cheers,
>
> Han Holl
>
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>
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83