Question

我正在尝试构建一个在FROM语句中使用JOIN语句别名的PostGIS查询，但这是不可能的。还有其他办法吗？

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

您可以引入额外级别的子查询。

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

（我改变了缩进以使它更有意义，虽然我仍然不理解它：你似乎没有使用b中任何地方的值）。你需要这样的东西：

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

你为什么不试试：

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;

这也可能有用：

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);

您可能想要验证（）的位置，因为我无法测试它。

在FROM中使用JOIN语句中的别名

2 个答案: