The SE_SpatialKey() function

The SE_SpatialKey() function generates a sort key for an ST_Geometry. A sort key is a numeric value that can be used to sort spatial objects according to their proximity to one another.

The sort key is computed by applying the Hilbert space-filling curve algorithm to the center point of an object's bounding box.

Syntax

SE_SpatialKey(g1 ST_Geometry)

Return type

A numeric sort key, as an INT8

Example

Create and populate a cities table containing the names and locations of world cities: 
CREATE TABLE cities (name varchar(255),
                     locn ST_Point);

LOAD FROM cities.load INSERT INTO cities;
Create a clustered functional B-tree index. This rearranges the table data, placing it in spatial key sort order. R-tree indexes, provides information about using indexes, in particular, R-tree indexes. For example: 
CREATE CLUSTER INDEX cbt_idx ON cities (SE_SpatialKey(locn));
Create an R-tree index with the NO_SORT option: 
CREATE INDEX locn_idx ON cities (locn ST_Geometry_ops)
  USING RTREE (BOTTOM_UP_BUILD='yes', NO_SORT='yes');
Drop the B-tree index; it is no longer needed: 
DROP INDEX cbt_idx;