CTE 的聚合列不能在 PostgreSQL 查询的 WHERE 子句中使用

Question

我的查询遵循以下结构：

WITH CTE AS (
    SELECT t1.x, COUNT(t1.y) AS count
    FROM table1 t1
    GROUP BY t1.x
)
SELECT CTE.x, CTE.count AS newCount, t2.count AS oldCount
FROM table2 t2 JOIN CTE ON t2.x = CTE.x
WHERE t2.count != CTE.count;

我收到以下错误：[42803] ERROR: aggregate functions are not allowed in WHERE

看起来是CTE.count触发此错误的聚合。CTE 不是应该在主查询之前计算吗？如何重写查询以避免这种情况？

x86_64-pc-linux-gnu 上的 PostgreSQL 13.2，由 gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5) 编译，64 位

Answer 1

被t2.count解释为聚合 COUNT() 函数，并且您的 t2 表没有名为 的列count。

确保您的表确实有一count列，或者确保在加入之前计算另一个 CTE 上的聚合计数，然后比较结果。还要避免使用别名“count”，如下所示：

WITH CTE AS (
    SELECT t1.x, COUNT(t1.y) AS total
    FROM table1 t1
    GROUP BY t1.x
),
CTE2 AS (
    SELECT t2.x, COUNT(t2.y) AS total
    FROM table2 t2
    GROUP BY t2.x
)
SELECT 
    CTE1.x, 
    CTE1.total AS newCount, 
    CTE2.total AS oldCount
FROM 
    CTE2 
    JOIN CTE1 ON CTE2.x = CTE1.x
WHERE 
    CTE2.total != CTE1.total;