出现 "not a single-group group function" 错误。所有非聚合列均已按以下方式列在组中

Question

SELECT    STATUS, 
          AVG(COUNT(CRIME_ID)) "Avg # of Crimes per Status"
FROM      CRIMES
GROUP BY  STATUS;

当我尝试运行时，我得到“不是按功能分组的单组”。如您所见，我已将非聚合列包含在分组依据列表中。当它从 SELECT 列表中删除时，它运行s，但我需要运行它。有什么问题？

Answer 1

Oracle 不允许在选择组时以这种方式嵌套两个聚合函数。子查询计数查询，然后取平均值：

SELECT AVG(cnt)
FROM
(
    SELECT STATUS, COUNT(CRIME_ID) AS cnt
    FROM CRIMES
    GROUP BY STATUS
) t;

请注意，您可以尝试：

SELECT AVG(COUNT(CRIME_ID)) OVER () AS avg
FROM CRIMES
GROUP BY STATUS
ORDER BY STATUS
OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY;

这里我们使用 AVG() 作为结果集中所有组的分析函数。然后，我们将输出限制为一行。

Answer 2

Oracle 实际上确实允许从其早期版本中嵌套两个聚合函数，但这样做意味着有两个聚合，第一个带有 GROUP BY 子句，而后一个没有。
这意味着我们不能 select GROUP BY -
中的列这就是错误的来源。

通过从 SELECT 子句中删除 STATUS 列，我们得到一个有效的查询：

SELECT    AVG(COUNT(CRIME_ID)) "Avg # of Crimes per Status"
FROM      CRIMES
GROUP BY  STATUS;

Avg # of Crimes per Status
3.33333333333333333333333333333333333333

Fiddle

"You can nest aggregate functions. For example, the following example calculates the average of the maximum salaries of all the departments in the scott schema:

SELECT AVG(MAX(salary)) FROM employees GROUP BY department_id;

AVG(MAX(SALARY))
`----------------
10925

This calculation evaluates the inner aggregate (MAX(sal)) for each group defined by the GROUP BY clause (deptno), and aggregates the results again."

Oracle9i SQL Reference Release 1 (9.0.1)

出现 "not a single-group group function" 错误。所有非聚合列均已按以下方式列在组中

Getting a "not a single-group group function" error. All non-aggregate columns have been listed in the group by

sql

oracle

group-by

ora-00937