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18.6.1. Creating Spatial Indexes

MySQL can create spatial indexes using syntax similar to that for creating regular indexes, but extended with the SPATIAL keyword. Currently, spatial columns that are indexed must be declared NOT NULL. The following examples demonstrate how to create spatial indexes:

  • With CREATE TABLE:

    CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g));
    
  • With ALTER TABLE:

    ALTER TABLE geom ADD SPATIAL INDEX(g);
    
  • With CREATE INDEX:

    CREATE SPATIAL INDEX sp_index ON geom (g);
    

For MyISAM tables, SPATIAL INDEX creates an R-tree index. For other storage engines that support spatial indexing, SPATIAL INDEX creates a B-tree index. A B-tree index on spatial values will be useful for exact-value lookups, but not for range scans.

To drop spatial indexes, use ALTER TABLE or DROP INDEX:

  • With ALTER TABLE:

    ALTER TABLE geom DROP INDEX g;
    
  • With DROP INDEX:

    DROP INDEX sp_index ON geom;
    

Example: Suppose that a table geom contains more than 32,000 geometries, which are stored in the column g of type GEOMETRY. The table also has an AUTO_INCREMENT column fid for storing object ID values.

mysql> DESCRIBE geom;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| fid   | int(11)  |      | PRI | NULL    | auto_increment |
| g     | geometry |      |     |         |                |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> SELECT COUNT(*) FROM geom;
+----------+
| count(*) |
+----------+
|    32376 |
+----------+
1 row in set (0.00 sec)

To add a spatial index on the column g, use this statement:

mysql> ALTER TABLE geom ADD SPATIAL INDEX(g);
Query OK, 32376 rows affected (4.05 sec)
Records: 32376  Duplicates: 0  Warnings: 0

 
 
  Published under the terms of the GNU General Public License Design by Interspire