On 6 September 2013 16:38, Pepijn Van Eeckhoudt <pep...@vaneeckhoudt.net> wrote:
> Hi,
>
> In the extension I'm developing (https://bitbucket.org/luciad/libgpkg)
> I'm currently adding support for queries like:
> select Distance(
> GeomFromText('Point(13.457 3)'),
> geometry
> ) from table;
>
> GeomFromText takes a string and outputs a geometry blob
> Distance takes two geometry blobs and returns a double
>
> In order to speed up the distance function I was wondering if I could
> use aux_data to cache the parsed version of the first parameter since
> this remains the same for every call. So far I haven't been able to get
> this to work though, aux_data is always NULL, no matter what I try.
>
> My hunch is that this is because the first parameter is the result of a
> function call which could in theory return different values for each row
> even if the input parameters are constant. Is that correct?
>
> Are there any other ways to kind of memoize the GeomFromText function
> (or the parameters to distance) besides aux_data?
select Distance( constGeom, geometry ) from table, (select
GeomFromText('Point(13.457 3)') as constGeom );
>
> Thanks,
>
> Pepijn
>
Regards,
Simon
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