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List:       postgresql-sql
Subject:    [SQL] Re: performance issue with distance function
From:       Mark kirkwood <markir () slingshot ! co ! nz>
Date:       2001-07-29 4:30:13
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Hi Ryan,

There is a bit of a strange way around the distance overhead issue :

Create another table with structure like 
(lat1,long1,zip1,lat2,long2,zip2,distance)

and precalculate the distance for each possibility. This means n*(n-1) rows 
if you have n location rows. You would then include this table in your query 
and use distance like you wanted to initially ( should work fast provided you 
index it on lat1,long1,distance)

The calculation overhead of distance is then removed from your query ( at the 
expense of some disk space ). The insert of each new location requires n 
calculations of distance - you could perform this in the background I guess !

regards

Mark


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