如何在一个查询中包含三个几何图形 - PostGIS

Question

我是 SQL 的新手，我在创建包含三个几何图形的查询时遇到困难。我有一个点层（建筑物），我想从中计算所有点建筑物，它们与某个多边形（市政单位）中的线（道路）的最大距离为 50 米，使用两个额外的标准三个 tables.

这是 table 结构：

Table 1: building (id_building, address_name,color_tagged,point)
Table 2: roads (id_road, line) 
Table 3: munic_units (id_munic, munic_name, polygon)

我尝试了下面的代码并做了很多更改..但是它给我错误。我很乐意听到任何建议。谢谢你。

SELECT address_name, count(*) AS Frequency,munic_name,color_tagged
FROM building,roads,munic_units 
WHERE ST_CONTAINS((SELECT polygon FROM munic_units WHERE munic_name=''),(ST_DWithin((SELECT point FROM building WHERE color_tagged=''),line,50))) 
GROUP BY address_name,munic_name,color_tagged 
ORDER BY Frequency DESC,address_name DESC;

首先，我尝试了一个具有两个几何形状的更简单的版本：

SELECT address_name, count(*) AS Frequency,color_tagged
FROM building,roads,loc_munic_units
WHERE ST_Dwithin(point,roads_geom,50) AND color_tagged='YELLOW'
GROUP BY address_name,color_tagged
ORDER BY Frequency DESC,address_name DESC;

和returns...enter image description here ..这个阶段的预期结果是找到距离道路50米以内的所有建筑物color_tagged作为'Yellow'。最终想要的结果是运行之前只在特定区域搜索 - tables 的一个 polygon.The 结构如下所示。

Answer 1

您已接近解决方案。第一个查询失败，因为您没有正确加入 tables。第二个查询可能 returns 高估了计数，因为您与城市 table.

进行了交叉连接

使用第二个查询，您可以添加缺少的连接条件（并正确编写连接）

SELECT address_name, count(*) AS Frequency,color_tagged
FROM building b  --selects from buildings
 JOIN roads r ON ST_Dwithin(b.point,r.roads_geom,50) -- when building is within 50 of a road
 JOIN loc_munic_units m ON ST_WITHIN(r.roads_geom, m.polygon) -- and when the road is within a municipality polygon
WHERE b.color_tagged='YELLOW' AND m.munic_name = 'abc' -- restrain to a specific municipality (or >1) and color
GROUP BY address_name,color_tagged
ORDER BY Frequency DESC,address_name DESC;

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