For MyISAM tables, MySQL can create
spatial indexes using syntax similar to that for creating
regular indexes, but extended with the
SPATIAL keyword. Currently, columns in
spatial indexes 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)) ENGINE=MyISAM;
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 storage engines
that support nonspatial indexing of spatial columns, the engine
creates a B-tree index. A B-tree index on spatial values will be
useful for exact-value lookups, but not for range scans.
For more information on indexing spatial columns, see
Section 12.1.11, “CREATE INDEX Syntax”.
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