[postgis-users] ST_Difference geom with NULL

[Chris Hermansen]

In the three state logic of true / false / unknown, null must be returned
from such an operation.

As strk says null represents unknown, not empty.
On Sep 10, 2011 6:12 AM, "Sandro Santilli" <strk at keybit.net> wrote:
> On Sat, Sep 10, 2011 at 3:08 PM, aperi2007 <aperi2007 at gmail.com> wrote:
>> Hi,
>>
>> using the postgis 2.00 svn ,
>>
>> I notice that the
>> ST_Difference(geom,NULL)
>> will return NULL.
>>
>> Instead
>> ST_Difference(geom, EMPTY)
>> will return the "geom" geometry
>>
>> Is this correct ?
>
> I think it is.
> NULL means "I don't know" while EMPTY means "I know it's nothing".
>
> --strk;
>
> Free GIS & Flash consultant/developer
> http://strk.keybit.net/services.html
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