使用空间索引
优化调查是否可用的空间索引可以参与的搜索使用的功能,如查询,MBRContains()
或MBRWithin()
中WHERE
的条款。以下查询查找给定矩形中的所有对象:
mysql>SET @poly = -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))'; mysql>SELECT fid,ST_AsText(g)FROM geomWHERE -> MBRContains(ST_GeomFromText(@poly),g); +----- +--------------------------------------------------------------- + | fid | ST_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)
使用EXPLAIN
检查执行该查询方式:
mysql>SET @poly = -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))'; mysql>EXPLAIN SELECT fid,ST_AsText(g)FROM geomWHERE -> MBRContains(ST_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)
检查没有空间索引会发生什么:
mysql>SET @poly = -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))'; mysql>EXPLAIN SELECT fid,ST_AsText(g)FROM gIGNORE INDEX (g)WHERE -> MBRContains(ST_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)
在SELECT
没有空间索引的情况下执行语句会产生相同的结果,但会使执行时间从0.00秒增加到0.46秒:
mysql>SET @poly = -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 15000))'; mysql>SELECT fid,ST_AsText(g)FROM geomIGNORE INDEX (g)WHERE -> MBRContains(ST_GeomFromText(@poly),g); +----- +--------------------------------------------------------------- + | fid | ST_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)