On 2/6/07, Jochem van Dieten <[EMAIL PROTECTED]> wrote:
>
>
> This query is not indexable so it needs to do the math on each and every
> row. Prequalify the rows by drawing an imaginary box on the map from
> b.lat + X to b.lat -X and b.lon + X to b.lon -X and finding only the
> points in that box (the database can do that using an index). Then
> perform your distance function only on the points in the box.
I did this to speed it up originally:
SELECT B.zipcode
FROM zipcodes B
WHERE
B.zipcode between '27002' and '28002'
getDistance('27502',0.0,0.0,'',B.latitude,B.longitude)
That caused it to only look at 1000 zip codes instead of 42000 zip codes.
the lat/long adjustment would probably be more effective.. or perhaps at
least, more accurate.
Rick
--
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