(mysql.info) using-a-spatial-index
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(mysql.info) creating-spatial-indexes
(mysql.info) optimizing-spatial-analysis
16.6.2 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 (the `id' column
has been removed so the output better fits the page):
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: range
possible_keys: g
key: g
key_len: 32
ref: NULL
rows: 50
Extra: Using where
1 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: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 32376
Extra: Using where
1 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)
In future releases, spatial indexes may also be used for optimizing
other functions. See
functions-for-testing-spatial-relations-between-geometric-objects.
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