PostGIS returns 记录为数据类型。这是出乎意料的

Question

我有这个问题

WITH buffered AS (
    SELECT 
        ST_Buffer(geom , 10, 'endcap=round join=round') AS geom,
        id
    FROM line),
hexagons AS (
    SELECT 
        ST_HexagonGrid(10, buffered.geom) AS hex,
        buffered.id
    FROM buffered
) SELECT * FROM hexagons;

这会在 hex 列中给出 datatype record。这是出乎意料的。我预计 geometry 为 datatype。这是为什么？

Answer 1

根据documentation，函数ST_HexagonGridreturns一个setof record。然而，这些记录包含一个名为 geom 的 geometry 属性，因此为了访问此 record 的 geometry，您必须用括号 () 和用点 . 调用属性，例如

SELECT (hex).geom FROM hexagons;

或使用 * 访问获取所有属性（在本例中，i、j 和 geom）：

SELECT (hex).* FROM hexagons;

演示（PostGIS 3.1）：

WITH j (hex) AS (
 SELECT 
  ST_HexagonGrid(
   10,ST_Buffer('LINESTRING(-105.55 41.11,-115.48 37.16,-109.29 29.38,-98.34 27.13)',1))    
)
SELECT ST_AsText((hex).geom,2) FROM j;

                                       st_astext                                        
----------------------------------------------------------------------------------------
 POLYGON((-130 34.64,-125 25.98,-115 25.98,-110 34.64,-115 43.3,-125 43.3,-130 34.64))
 POLYGON((-115 25.98,-110 17.32,-100 17.32,-95 25.98,-100 34.64,-110 34.64,-115 25.98))
 POLYGON((-115 43.3,-110 34.64,-100 34.64,-95 43.3,-100 51.96,-110 51.96,-115 43.3))
 POLYGON((-100 34.64,-95 25.98,-85 25.98,-80 34.64,-85 43.3,-95 43.3,-100 34.64))

作为 ST_HexagonGrid returns a setof record，您可以使用 LATERAL 访问记录属性，如 here 所述，或者只调用函数FROM 子句：

SELECT i,j,ST_AsText(geom,2) FROM 
  ST_HexagonGrid(
   10,ST_Buffer('LINESTRING(-105.55 41.11,-115.48 37.16,-109.29 29.38,-98.34 27.13)',1));

 i  | j |                                       st_astext                                        
----+---+----------------------------------------------------------------------------------------
 -8 | 2 | POLYGON((-130 34.64,-125 25.98,-115 25.98,-110 34.64,-115 43.3,-125 43.3,-130 34.64))
 -7 | 1 | POLYGON((-115 25.98,-110 17.32,-100 17.32,-95 25.98,-100 34.64,-110 34.64,-115 25.98))
 -7 | 2 | POLYGON((-115 43.3,-110 34.64,-100 34.64,-95 43.3,-100 51.96,-110 51.96,-115 43.3))
 -6 | 2 | POLYGON((-100 34.64,-95 25.98,-85 25.98,-80 34.64,-85 43.3,-95 43.3,-100 34.64))

进一步阅读：How to divide world into cells (grid)

PostGIS returns 记录为数据类型。这是出乎意料的

PostGIS returns record as datatype. This is unexpected

postgresql

postgis