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11.5.11 Using Spatial Indexes

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:

  1. mysql> SET @poly =
  2.     -> 'Polygon((30000 15000,
  3.                 31000 15000,
  4.                 31000 16000,
  5.                 30000 16000,
  6.                 30000 15000))';
  7. mysql> SELECT fid,ST_AsText(g) FROM geom WHERE
  8.     -> MBRContains(ST_GeomFromText(@poly),g);
  9. +-----+---------------------------------------------------------------+
  10. | fid | ST_AsText(g)                                                  |
  11. +-----+---------------------------------------------------------------+
  12. |  21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30 ... |
  13. |  22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8, ... |
  14. |  23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4, ... |
  15. |  24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4, ... |
  16. |  25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882. ... |
  17. |  26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4, ... |
  18. | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946. ... |
  19. |   1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136. ... |
  20. |   2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136, ... |
  21. |   3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,3016 ... |
  22. |   4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30 ... |
  23. |   5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4, ... |
  24. |   6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,3024 ... |
  25. |   7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8, ... |
  26. |  10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6, ... |
  27. |  11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2, ... |
  28. |  13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,3011 ... |
  29. | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30 ... |
  30. | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30 ... |
  31. | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4, ... |
  32. +-----+---------------------------------------------------------------+
  33. 20 rows in set (0.00 sec)

Use EXPLAIN to check the way this query is executed:

  1. mysql> SET @poly =
  2.     -> 'Polygon((30000 15000,
  3.                 31000 15000,
  4.                 31000 16000,
  5.                 30000 16000,
  6.                 30000 15000))';
  7. mysql> EXPLAIN SELECT fid,ST_AsText(g) FROM geom WHERE
  8.     -> MBRContains(ST_GeomFromText(@poly),g)\G
  9. *************************** 1. row ***************************
  10.            id: 1
  11.   select_type: SIMPLE
  12.         table: geom
  13.          type: range
  14. possible_keys: g
  15.           key: g
  16.       key_len: 32
  17.           ref: NULL
  18.          rows: 50
  19.         Extra: Using where
  20. 1 row in set (0.00 sec)

Check what would happen without a spatial index:

  1. mysql> SET @poly =
  2.     -> 'Polygon((30000 15000,
  3.                 31000 15000,
  4.                 31000 16000,
  5.                 30000 16000,
  6.                 30000 15000))';
  7. mysql> EXPLAIN SELECT fid,ST_AsText(g) FROM g IGNORE INDEX (g) WHERE
  8.     -> MBRContains(ST_GeomFromText(@poly),g)\G
  9. *************************** 1. row ***************************
  10.            id: 1
  11.   select_type: SIMPLE
  12.         table: geom
  13.          type: ALL
  14. possible_keys: NULL
  15.           key: NULL
  16.       key_len: NULL
  17.           ref: NULL
  18.          rows: 32376
  19.         Extra: Using where
  20. 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:

  1. mysql> SET @poly =
  2.     -> 'Polygon((30000 15000,
  3.                 31000 15000,
  4.                 31000 16000,
  5.                 30000 16000,
  6.                 30000 15000))';
  7. mysql> SELECT fid,ST_AsText(g) FROM geom IGNORE INDEX (g) WHERE
  8.     -> MBRContains(ST_GeomFromText(@poly),g);
  9. +-----+---------------------------------------------------------------+
  10. | fid | ST_AsText(g)                                                  |
  11. +-----+---------------------------------------------------------------+
  12. |   1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136. ... |
  13. |   2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136, ... |
  14. |   3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,3016 ... |
  15. |   4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30 ... |
  16. |   5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4, ... |
  17. |   6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,3024 ... |
  18. |   7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8, ... |
  19. |  10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6, ... |
  20. |  11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2, ... |
  21. |  13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,3011 ... |
  22. |  21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30 ... |
  23. |  22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8, ... |
  24. |  23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4, ... |
  25. |  24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4, ... |
  26. |  25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882. ... |
  27. |  26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4, ... |
  28. | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30 ... |
  29. | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30 ... |
  30. | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4, ... |
  31. | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946. ... |
  32. +-----+---------------------------------------------------------------+
  33. 20 rows in set (0.46 sec)

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Document created the 26/06/2006, last modified the 26/10/2018
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