PostgreSQL：如果下一个查询与上一个查询相交，则排除下一个查询的几何

Question

我有这个查询来获取在另一个几何中相交的几何数量：

SELECT  count(evidensapp_polystructures.brgy_locat) AS high,
        evidensapp_polystructures.brgy_locat AS barangay,
        evidensapp_polystructures.municipali AS municipality
FROM evidensapp_floodhazard
INNER JOIN evidensapp_polystructures
      ON st_intersects(evidensapp_floodhazard.geom, evidensapp_polystructures.geom) 
      AND evidensapp_floodhazard.hazard= 'High'
GROUP BY evidensapp_polystructures.brgy_locat, evidensapp_polystructures.municipali;

您已经注意到，它的hazard等于High 。 我还想获得与hazard值相交的几何数量： Medium和Low 。 但是，如果某个几何图形已在High中相交，则将其排除在Medium查询之外，与Low相同的情况将排除那些在High和Medium相交的几何。

我有这个想法，也许使用CASE，或者我需要获取几何的id ，然后尝试在查询中NOT IN ，但不知道该怎么做。 可能是因为我是PostgreSQL的新手或任何数据库工作。

这是上面查询的示例结果：

预期结果应如下所示：

表格详情：

CREATE TABLE evidensapp_floodhazard (
  id serial NOT NULL,
  hazard character varying(6) NOT NULL,
  date_field character varying(60),
  geom geometry(MultiPolygon,32651),
  CONSTRAINT evidensapp_floodhazard_pkey PRIMARY KEY (id)
);

CREATE INDEX evidensapp_floodhazard_geom_id
  ON evidensapp_floodhazard USING gist (geom);

ALTER TABLE evidensapp_floodhazard CLUSTER ON evidensapp_floodhazard_geom_id;

CREATE TABLE evidensapp_polystructures (
  id serial NOT NULL,
  bldg_name character varying(100) NOT NULL,
  bldg_type character varying(50) NOT NULL,
  brgy_locat character varying(50) NOT NULL,
  municipali character varying(50) NOT NULL,
  province character varying(50) NOT NULL,
  geom geometry(MultiPolygon,32651),
  CONSTRAINT evidensapp_polystructures_pkey PRIMARY KEY (id)
);

CREATE INDEX evidensapp_polystructures_geom_id
  ON evidensapp_polystructures USING gist (geom);

ALTER TABLE evidensapp_polystructures CLUSTER ON evidensapp_polystructures_geom_id;

Answer 1

由于就比较而言，您几乎无法使用字符串“ High”，“ Medium”和“ Low”，因此必须使用子查询。 带有某些CTE的解决方案可能是最干净的：

WITH hi AS (
  SELECT ps.id, ps.brgy_locat, ps.municipali
  FROM evidensapp_polystructures ps
  JOIN evidensapp_floodhazard fh ON fh.hazard = 'High'
                                 AND ST_Intersects(fh.geom, ps.geom)
), med AS (
  SELECT ps.id, ps.brgy_locat, ps.municipali
  FROM evidensapp_polystructures ps
  JOIN evidensapp_floodhazard fh ON fh.hazard = 'Medium'
                                 AND ST_Intersects(fh.geom, ps.geom)
  EXCEPT SELECT * FROM hi
), low AS (
  SELECT ps.id, ps.brgy_locat, ps.municipali
  FROM evidensapp_polystructures ps
  JOIN evidensapp_floodhazard fh ON fh.hazard = 'Low'
                                 AND ST_Intersects(fh.geom, ps.geom)
  EXCEPT SELECT * FROM hi
  EXCEPT SELECT * FROM med
)
SELECT brgy_locat AS barangay, municipali AS municipality, high, medium, low
FROM (SELECT brgy_locat, municipali, count(*) AS high
      FROM hi
      GROUP BY 1, 2) cnt_hi
FULL JOIN (SELECT brgy_locat, municipali, count(*) AS medium
      FROM med
      GROUP BY 1, 2) cnt_med USING (brgy_locat, municipali)
FULL JOIN (SELECT brgy_locat, municipali, count(*) AS low
      FROM low
      GROUP BY 1, 2) cnt_low USING (brgy_locat, municipali);

在三个CTE中，您首先确定属于“高”危险类别的行，然后确定属于“中”危险类别的行，但要EXCEPT已经属于“高”类别的行，然后是属于“低”危险类别的行，除了列为“高”或“中”的那些。 然后，在主查询中，将3个CTE与每个子CTE的子查询中计算的每个barangay和自治市的计数相结合。 使用FULL JOIN可以使结果中不显示具有“高”危险等级结构的Barangays和市政当局。