Re: Designing an extension for feature-space similarity search

Alexander Korotkov wrote:
> On Fri, Feb 17, 2012 at 11:00 PM, Jay Levitt <jay.levitt@gmail.com
> <mailto:jay.levitt@gmail.com>> wrote:
>    At first I thought this posed a challenge for union; if I have these 
points:
>
>     (1,2)
>     (2,1)
>     (1,NULL)
>
>     what's the union? I think the answer is to treat NULL box coordinates
>     like LL = -infinity, UR = infinity, or (equivalently, I think) to store
>     a saw_nulls bit in addition to LL and UR.
>
> Similar problem appears at GiST indexing of ranges, because range can be
> empty. There additional "contain empty" flag was introduced. This "contain
> empty" flag indicates that underlying value can be empty. So, this flag is
> set when union with empty range or other range with this flag set. It's
> likely you need similar flag for each dimension.

Ah, yes, exactly the same problem. So what led you to add a flag instead of 
using the range NULL..NULL? I'm on the fence about choosing.

Jay