PostgreSQL：如果下一個查詢與上一個查詢相交，則排除下一個查詢的幾何

Question

我有這個查詢來獲取在另一個幾何中相交的幾何數量：

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;

您已經注意到，它的hazard等於High 。 我還想獲得與hazard值相交的幾何數量： Medium和Low 。 但是，如果某個幾何圖形已在High中相交，則將其排除在Medium查詢之外，與Low相同的情況將排除那些在High和Medium相交的幾何。

我有這個想法，也許使用CASE，或者我需要獲取幾何的id ，然后嘗試在查詢中NOT IN ，但不知道該怎么做。 可能是因為我是PostgreSQL的新手或任何數據庫工作。

這是上面查詢的示例結果：

預期結果應如下所示：

表格詳情：

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

由於就比較而言，您幾乎無法使用字符串“ High”，“ Medium”和“ Low”，因此必須使用子查詢。 帶有某些CTE的解決方案可能是最干凈的：

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);

在三個CTE中，您首先確定屬於“高”危險類別的行，然后確定屬於“中”危險類別的行，但要EXCEPT已經屬於“高”類別的行，然后是屬於“低”危險類別的行，除了列為“高”或“中”的那些。 然后，在主查詢中，將3個CTE與每個子CTE的子查詢中計算的每個barangay和自治市的計數相結合。 使用FULL JOIN可以使結果中不顯示具有“高”危險等級結構的Barangays和市政當局。