优化程序将调查可用的空间索引是否能包含在使用某些函数的查询搜索中，如WHERE子句中的MBRContains()或MBRWithin()函数。例如，假定我们打算找出位于给定矩形中的所有对象：
mysql> SELECT fid,AsText(g) FROM geom WHERE
mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);
+-----+-----------------------------------------------------------------------------+
| fid | AsText(g) |
+-----+-----------------------------------------------------------------------------+
| 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) |
| 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) |
| 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) |
| 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) |
| 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) |
| 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) |
| 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) |
| 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) |
| 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) |
| 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) |
| 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) |
| 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) |
| 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) |
| 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) |
| 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) |
| 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) |
| 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) |
| 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) |
| 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) |
| 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) |
+-----+-----------------------------------------------------------------------------+
20 rows in set (0.00 sec)
我们使用EXPLAIN来检查该查询的执行方式（ID列已被删除，以便输出能更好地与页匹配）：
mysql> EXPLAIN SELECT fid,AsText(g) FROM geom WHERE
mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);
+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| SIMPLE | geom | range | g | g | 32 | NULL | 50 | Using where |
+-------------+-------+-------+---------------+------+---------+------+------+-------------+
1 row in set (0.00 sec)
让我们检查一下在没有空间索引的情况下会出现什么：
mysql> EXPLAIN SELECT fid,AsText(g) FROM g IGNORE INDEX (g) WHERE
mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);
+-------------+-------+------+---------------+------+---------+------+-------+-------------+
| select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+-------------+-------+------+---------------+------+---------+------+-------+-------------+
| SIMPLE | geom | ALL | NULL | NULL | NULL | NULL | 32376 | Using where |
+-------------+-------+------+---------------+------+---------+------+-------+-------------+
1 row in set (0.00 sec)
执行SELECT语句，忽略空间键：
mysql> SELECT fid,AsText(g) FROM geom IGNORE INDEX (g) WHERE
mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);
+-----+-----------------------------------------------------------------------------+
| fid | AsText(g) |
+-----+-----------------------------------------------------------------------------+
| 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) |
| 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) |
| 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) |
| 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) |
| 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) |
| 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) |
| 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) |
| 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) |
| 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) |
| 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) |
| 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) |
| 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) |
| 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) |
| 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) |
| 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) |
| 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) |
| 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) |
| 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) |
| 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) |
| 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) |
+-----+-----------------------------------------------------------------------------+
20 rows in set (0.46 sec)
未使用索引时，该查询的执行时间将从0.00秒上升到0.46秒。
在未来的版本中，空间索引也可能会用于优化其他函数。请参见19.5.4节，“测试几何对象间空间关系的函数”。
