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:
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With
CREATE TABLE:CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g)) ENGINE=MyISAM;
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With
ALTER TABLE:ALTER TABLE geom ADD SPATIAL INDEX(g);
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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 13.1.8, “CREATE INDEX Syntax”.
To drop spatial indexes, use ALTER TABLE or DROP INDEX:
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With
ALTER TABLE:ALTER TABLE geom DROP INDEX g;
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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