PostgreSQL“列不存在”错误CartoDB

Question

我目前正在处理一个查询，该查询应该返回一个按照邻近给定点排序的CartoDB表（即新表）的子集。我想，通过使用PostgreSQL的ROW_NUMBER（）方法，在新的一列显示对应到最近在地图上的标签，第二最接近等，想捕捉：

SELECT 
    *, 
    ST_Distance(
     ST_GeomFromText('Point(-73.95623080000001 40.6738101)', 4326)::geography, 
     the_geom::geography 
    )/1609 AS dist, 
    row_number() OVER (ORDER BY dist) as rownum 
FROM locations 
WHERE ST_Intersects(
    ST_GeomFromText(
     'Point(-73.95623080000001 40.6738101)', 4326 
    ), 
    the_geom 
) 
ORDER BY dist ASC 

然而，当我尝试这一点， CartoDB/PostgreSQL返回以下错误：

Error: column "dist" does not exist 

任何关于更好的方法或我失踪的建议？

Answer 1

您CANT使用在同一级别上计算的字段。

SELECT (x1-x2)^2 + (y1-x2)^2 as dist, dist * 1.6 as miles 
             ^^^^^ 
            undefined 

所以你创建一个子查询。

SELECT dist * 1.6 as miles 
FROM (SELECT (x1-x2)^2 + (y1-x2)^2 as dist 
     FROM table 
    ) T 

Answer 2

您不能在另一列中使用列别名。在这里，您将定义dist作为结果列表，并将其用于row_number的ORDER BY。您必须编写与order相同的表达式。

Answer 3

SELECT *, 
    row_number() OVER (ORDER BY dist) as rownum 
FROM(
SELECT 
    *, 
    ST_Distance(
     ST_GeomFromText('Point(-73.95623080000001 40.6738101)', 4326)::geography, 
     the_geom::geography 
    )/1609 AS dist 
FROM locations 
WHERE ST_Intersects(
    ST_GeomFromText(
     'Point(-73.95623080000001 40.6738101)', 4326 
    ), 
    the_geom 
) 
) i 
ORDER BY dist ASC 

您不能从同一个访问的别名选择所以把它放在一个内部查询

Answer 4

内虽然可以使用派生内部查询（这可能是更容易阅读和可能根据其他RA规则进行优化），也可以使用序号来指代列，因为限制仅适用于新引入的名称。

例如，以下是有效的：

SELECT 
    ST_Distance(
     ST_GeomFromText('Point(-73.95623080000001 40.6738101)', 4326)::geography, 
     the_geom::geography 
    )/1609 AS dist 
    -- column ordering changed to make ordinal obvious, as * can bite 
    -- now column 'dist' is the first column and can be referenced by ordinal 
    , row_number() OVER (ORDER BY 1) as rownum 
    , * 
FROM locations 
WHERE ST_Intersects(
    ST_GeomFromText(
     'Point(-73.95623080000001 40.6738101)', 4326 
    ), 
    the_geom 
) 
-- this could also be written as ORDER BY 1 ASC, per ordinal 
ORDER BY dist ASC