使用別名FROM FROM中的JOIN語句

Question

我試圖構建一個PostGIS查詢，它在FROM語句中使用JOIN語句的別名，但這是不可能的。還有另一種方法可以做到嗎？

SELECT DISTINCT 
ST_Buffer(
    ST_Centroid(geom), 
    ST_Area(geom)) 
FROM building AS b, ST_Transform(sg.geometry, 31467) AS geom 
LEFT JOIN surface_geometry AS sg ON b.id = sg.cityobject_id WHERE ST_Area(geom) < 100 

Answer 1

您可以引入額外級別的子查詢。

所以目前你有：

SELECT DISTINCT ST_Buffer(ST_Centroid(geom), ST_Area(geom)) 
FROM building AS b, 
    ST_Transform(sg.geometry, 31467) AS geom 
    LEFT JOIN surface_geometry AS sg ON b.id = sg.cityobject_id 
WHERE ST_Area(geom) < 100 

（我改變了縮進，使更多一點它的意義，但我還是不明白：你似乎沒有從B使用的值任何地方）。你需要這樣的東西：

SELECT DISTINCT ST_Buffer(ST_Centroid(geom), ST_Area(geom)) 
FROM (
    SELECT ST_Transform(sg.geometry, 31467) AS geom 
    FROM building AS b 
     LEFT JOIN surface_geometry AS sg ON b.id = sg.cityobject_id 
) x 
WHERE ST_Area(geom) < 100 

Answer 2

爲什麼你會不會嘗試：

SELECT DISTINCT 
    ST_Buffer(ST_Centroid(ST_Transform(sg.geometry, 31467), 
       ST_Area(ST_Transform(sg.geometry, 31467))) 
FROM building b LEFT JOIN surface_geometry sg ON (b.id = sg.cityobject_id) 
WHERE ST_Area(ST_Transform(sg.geometry, 31467)) < 100; 

也有可能，這可能工作：

SELECT DISTINCT 
    ST_Buffer(ST_Centroid(geom), ST_Area(geom)) 
FROM building b LEFT JOIN surface_geometry sg ON (b.id = sg.cityobject_id) INNER JOIN 
    ST_Transform(surface_geometry.geometry, 31467) geom ON (ST_Area(geom) < 100); 

您可能需要驗證的（安置）作爲目前我沒地方去測試它。