Postgres - 两个查询的减法

Question

我想做这样的减法：

SELECT 
    (SELECT ST_Y(ST_Centroid(ST_Collect(column1))) AS distance_km 
     FROM table1) - 
    (SELECT ST_Y(ST_Transform(column1,4326)) AS distance_km 
     FROM table1) AS Difference

但是ST_Y(ST_Centroid(ST_Collect(column1)))只有一行而ST_Y(ST_Transform(column1,4326))有多行。我想按列减去多行并查看每多行的结果。通过此查询，我得到：

ERROR: more than one row returned by a subquery used as an expression

有什么帮助吗？

Answer 1

以下查询会将单行结果集与多行结果集相结合，并允许对它们进行比较。

SELECT
    a.*,
    b.*,
    a.distance_km - b.distance_kn    AS difference
FROM
(
    SELECT  ST_Y(ST_Centroid(ST_Collect(column1))) AS distance_km FROM table1
)
    a
CROSS JOIN
(
    SELECT ST_Y(ST_Transform(column1,4326)) AS distance_km FROM table1
)
    b

Postgres - 两个查询的减法

Postgres - Subtraction of two queries

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