sql – PostGis最近邻查询

我想检索另一组点的给定范围内的所有点.比方说,找到距离任何地铁站500米范围内的所有商店.

我写了这个查询,这很慢,并且想要优化它：

SELECT disCTINCT ON(locations.id) locations.id FROM locations,pois
WHERE pois.poi_kind = 'subway'
AND ST_DWithin(locations.coordinates,pois.coordinates,500,false);

我正在运行最新版本的Postgres和PostGis(Postgres 9.5,PostGis 2.2.1)

这是表元数据：

Table "public.locations"
       Column       |            Type             |                       Modifiers
--------------------+-----------------------------+--------------------------------------------------------
 id                 | integer                     | not null default nextval('locations_id_seq'::regclass)
 coordinates        | geometry                    |
Indexes:
    "locations_coordinates_index" gist (coordinates)


                                      Table "public.pois"
   Column    |            Type             |                     Modifiers
-------------+-----------------------------+---------------------------------------------------
 id          | integer                     | not null default nextval('pois_id_seq'::regclass)
 coordinates | geometry                    |
 poi_kind_id | integer                     |
Indexes:
    "pois_pkey" PRIMARY KEY,btree (id)
    "pois_coordinates_index" gist (coordinates)
    "pois_poi_kind_id_index" btree (poi_kind_id)
Foreign-key constraints:
    "pois_poi_kind_id_fkey" FOREIGN KEY (poi_kind_id) REFERENCES poi_kinds(id)

这是EXPLAIN(ANALYZE,BUFFERS)的结果：

Unique  (cost=2407390.71..2407390.72 rows=2 width=4) (actual time=3338.080..3338.252 rows=918 loops=1)
Buffers: shared hit=559
->  Sort  (cost=2407390.71..2407390.72 rows=2 width=4) (actual time=3338.079..3338.145 rows=963 loops=1)
      Sort Key: locations.id
      Sort Method: quicksort  Memory: 70kB
      Buffers: shared hit=559
      ->  nested Loop  (cost=0.00..2407390.71 rows=2 width=4) (actual time=2.466..3337.835 rows=963 loops=1)
            Join Filter: (((pois.coordinates)::geography && _st_expand((locations.coordinates)::geography,500::double precision)) AND ((locations.coordinates)::geography && _st_expand((pois.coordinates)::geography,500::double precision)) AND _st_dwithin((pois.coordinates)::geography,(locations.coordinates)::geography,500::double precision,false))
            Rows Removed by Join Filter: 4531356
            Buffers: shared hit=559
            ->  Seq Scan on locations  (cost=0.00..791.68 rows=24168 width=36) (actual time=0.005..3.100 rows=24237 loops=1)
                  Buffers: shared hit=550
            ->  Materialize  (cost=0.00..10.47 rows=187 width=32) (actual time=0.000..0.009 rows=187 loops=24237)
                  Buffers: shared hit=6
                  ->  Seq Scan on pois  (cost=0.00..9.54 rows=187 width=32) (actual time=0.015..0.053 rows=187 loops=1)
                        Filter: (poi_kind_id = 3)
                        Rows Removed by Filter: 96
                        Buffers: shared hit=6
Planning time: 0.184 ms
Execution time: 3338.304 ms
(20 rows)

解决方法

我认为您使用的是st_dwithin的地理版本,因为第四个参数.

尝试将您的查询更改为此查询：

SELECT disCTINCT ON(locations.id) locations.id FROM locations,500);

如果没有解决,请再次发布解释分析.