Thanks, I'll give this a go...
Jigal van Hemert wrote:
> Ben Clewett wrote:
>> But the index does not seem nearly as fast as liner (normal) indexes.
>> Hence using a less effective liner index may be better...
>> After this method I still need select a radius within these data
>> points, more effort.
> This could be an excellent case for using HAVING <expr>
> The WHERE can use an index and be very fast selecting the records that
> might fall within the circle. The HAVING clause will be executed after
> the record set is built and remove the records outside the circle, but
> within the square. If the number of records you select is pretty limited
> (a few hundred or so) the POW() calculations will not ask too much from
> the server, but the full table scan is avoided...
> Regards, Jigal.