Question

I have a column of type geography. I have created a a spatial index, but its not being used:

declare @geog geography 
select @geog = 'POINT (18.12 -33.2)' 

select  *
from  dbo.product  WITH(INDEX(IX_Spatial))  
where 
@geog.STDistance(GeoLocation) > 1000

The index is created like this:

 CREATE SPATIAL INDEX [IX_Spatial] ON [dbo].[Product] 
(
 [GeoLocation]
)USING  GEOGRAPHY_GRID 
WITH (
GRIDS =(LEVEL_1 = MEDIUM,LEVEL_2 = MEDIUM,LEVEL_3 = MEDIUM,LEVEL_4 = MEDIUM), 
CELLS_PER_OBJECT = 1024, 
PAD_INDEX  = OFF, SORT_IN_TEMPDB = OFF, 
DROP_EXISTING = OFF, ALLOW_ROW_LOCKS  = ON, 
ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
GO

The values for grid density at the various levels are for not deliberately set to medium. It makes no difference what I set them to, If I view the estimated execution plan, the index is not used.

[http://blogs.msdn.com/b/isaac/archive/2008/08/29/is-my-spatial-index-being-used.aspx][1]

If I try to add a hint to the query optimizer

declare @geog geography 
select @geog = 'POINT (18.12 -33.2)' 

select  *
from  dbo.product  WITH(INDEX(IX_Spatial))  
where 
@geog.STDistance(GeoLocation) > 1000

I get this error:

The query processor could not produce
a query plan for a query with a
spatial index hint. Reason: Spatial
indexes do not support the comparator
supplied in the predicate

My database is running at SQL Server 2008 (100) compatibility level.

.

Answer 1

SQL Server creates spatial indexes in the following way: it splits the whole map into several rectangles (tiles) and indexes the number of each tile.

For any given point, it is possible to calculate the numbers of rectangles within a distance but not out of the distance (there can be infinitely many).