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:
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
