12.18.6.2. Using a Spatial Index

The optimizer investigates whether available spatial indexes can be involved in the search for queries that use a function such as MBRContains() or MBRWithin() in the WHERE clause. The following query finds all objects that are in the given rectangle:

mysql> SET @poly =    -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))';mysql> SELECT fid,AsText(g) FROM geom WHERE    -> MBRContains(GeomFromText(@poly),g);+-----+---------------------------------------------------------------+| fid | AsText(g)                                                     |+-----+---------------------------------------------------------------+|  21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30 ... ||  22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8, ... ||  23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4, ... ||  24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4, ... ||  25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882. ... ||  26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4, ... || 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946. ... ||   1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136. ... ||   2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136, ... ||   3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,3016 ... ||   4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30 ... ||   5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4, ... ||   6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,3024 ... ||   7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8, ... ||  10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6, ... ||  11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2, ... ||  13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,3011 ... || 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30 ... || 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30 ... || 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4, ... |+-----+---------------------------------------------------------------+20 rows in set (0.00 sec)

Use EXPLAIN to check the way this query is executed:

mysql> SET @poly =    -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))';mysql> EXPLAIN SELECT fid,AsText(g) FROM geom WHERE    -> MBRContains(GeomFromText(@poly),g)\G*************************** 1. row ***************************           id: 1  select_type: SIMPLE        table: geom         type: rangepossible_keys: g          key: g      key_len: 32          ref: NULL         rows: 50        Extra: Using where1 row in set (0.00 sec)

Check what would happen without a spatial index:

mysql> SET @poly =    -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))';mysql> EXPLAIN SELECT fid,AsText(g) FROM g IGNORE INDEX (g) WHERE    -> MBRContains(GeomFromText(@poly),g)\G*************************** 1. row ***************************           id: 1  select_type: SIMPLE        table: geom         type: ALLpossible_keys: NULL          key: NULL      key_len: NULL          ref: NULL         rows: 32376        Extra: Using where1 row in set (0.00 sec)

Executing the SELECT statement without the spatial index yields the same result but causes the execution time to rise from 0.00 seconds to 0.46 seconds:

mysql> SET @poly =    -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))';mysql> SELECT fid,AsText(g) FROM geom IGNORE INDEX (g)
        WHERE    -> MBRContains(GeomFromText(@poly),g);+-----+---------------------------------------------------------------+| fid | AsText(g)                                                     |+-----+---------------------------------------------------------------+|   1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136. ... ||   2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136, ... ||   3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,3016 ... ||   4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30 ... ||   5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4, ... ||   6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,3024 ... ||   7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8, ... ||  10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6, ... ||  11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2, ... ||  13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,3011 ... ||  21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30 ... ||  22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8, ... ||  23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4, ... ||  24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4, ... ||  25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882. ... ||  26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4, ... || 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30 ... || 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30 ... || 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4, ... || 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946. ... |+-----+---------------------------------------------------------------+20 rows in set (0.46 sec)