<->
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Name

<-> — 返回 A 和 B 之间的 2D 距离。

Synopsis

double precision <->( geometry A , geometry B );

double precision <->( geography A , geography B );

描述

The <-> operator returns the 2D distance between two geometries. Used in the "ORDER BY" clause provides index-assisted nearest-neighbor result sets with true KNN distance search for geometries, and distance on the sphere for geographies.

[Note]

该操作符将利用几何上可能可用的 2D GiST 索引。 它与其他使用空间索引的运算符不同，只有当该运算符位于 ORDER BY 子句中时才会使用空间索引。
[Note]

仅当其中一个几何图形是常量（不在子查询/cte 中）时，索引才会启动。 例如 'SRID=3005;POINT(1011102 450541)'::geometry 而不是 a.geom

有关详细示例，请参阅 PostGIS 研讨会：最近邻搜索。

Enhanced: 2.2.0 -- True KNN ("K nearest neighbor") behavior for geometry and geography. Note for geography KNN is based on sphere rather than spheroid.

Changed: 2.2.0 -- Old hybrid-syntax workarounds may be slower once true KNN is available. See examples below.

Availability: 2.0.0 -- Weak KNN provides nearest neighbors based on geometry centroid distances instead of true distances. Exact results for points, inexact for all other types.

示例

SELECT ST_Distance(geom, 'SRID=3005;POINT(1011102 450541)'::geometry) as d,edabbr, vaabbr
FROM va2005
ORDER BY d limit 10;

        d         | edabbr | vaabbr
------------------+--------+--------
                0 | ALQ    | 128
 5541.57712511724 | ALQ    | 129A
 5579.67450712005 | ALQ    | 001
  6083.4207708641 | ALQ    | 131
  7691.2205404848 | ALQ    | 003
 7900.75451037313 | ALQ    | 122
 8694.20710669982 | ALQ    | 129B
 9564.24289057111 | ALQ    | 130
  12089.665931705 | ALQ    | 127
 18472.5531479404 | ALQ    | 002
(10 rows)

KNN的原始答案是： 

SELECT st_distance(geom, 'SRID=3005;POINT(1011102 450541)'::geometry) as d,edabbr, vaabbr
FROM va2005
ORDER BY geom <-> 'SRID=3005;POINT(1011102 450541)'::geometry limit 10;

        d         | edabbr | vaabbr
------------------+--------+--------
                0 | ALQ    | 128
 5541.57712511724 | ALQ    | 129A
 5579.67450712005 | ALQ    | 001
  6083.4207708641 | ALQ    | 131
  7691.2205404848 | ALQ    | 003
 7900.75451037313 | ALQ    | 122
 8694.20710669982 | ALQ    | 129B
 9564.24289057111 | ALQ    | 130
  12089.665931705 | ALQ    | 127
 18472.5531479404 | ALQ    | 002
(10 rows)

如果您对这两个查询运行“EXPLAIN ANALYZE”，您将看到第二个查询的性能有所提高。

When a plan cannot produce exact distances directly, use a hybrid query to find the true nearest neighbors. First a CTE query using the index-assisted KNN, then an exact query to get correct ordering: 

WITH index_query AS (
  SELECT ST_Distance(geom, 'SRID=3005;POINT(1011102 450541)'::geometry) as d,edabbr, vaabbr
        FROM va2005
  ORDER BY geom <-> 'SRID=3005;POINT(1011102 450541)'::geometry LIMIT 100)
  SELECT *
        FROM index_query
  ORDER BY d limit 10;

        d         | edabbr | vaabbr
------------------+--------+--------
                0 | ALQ    | 128
 5541.57712511724 | ALQ    | 129A
 5579.67450712005 | ALQ    | 001
  6083.4207708641 | ALQ    | 131
  7691.2205404848 | ALQ    | 003
 7900.75451037313 | ALQ    | 122
 8694.20710669982 | ALQ    | 129B
 9564.24289057111 | ALQ    | 130
  12089.665931705 | ALQ    | 127
 18472.5531479404 | ALQ    | 002
(10 rows)

相关信息

ST_DWithin, ST_Distance, <#>