我怎样才能得到这张桌子的平均值？

Question

我有两栏

SQL> SELECT COUNT(A),CAR                                                        
  2  FROM ASIGNATURA                                                            
  3  GROUP BY CAR;                                                              

COUNT(A)        CAR

 1          1
 1          6
 1          2
 2          4
 1          5
 1          8
 4          7
 1          3

选择了8行。

SQL> SELECT AVG(COUNT(A)),CAR                                                   
2  FROM ASIGNATURA                                                            
3  GROUP BY CAR;                                                              


SELECT AVG(COUNT(A)),CAR                     *
ERROR at line 1:
ORA-00937: not a single-group group function

我希望两列的平均值如下：

 1/12   1
 1/12   6
 1/12   2
 2/12   4

 etc... 

我该怎么做？

Answer 1

您实际上并未计算平均值，而是将其显示为平均值。

尝试：

SELECT COUNT(CAR)
  ||'/'
  ||
  (SELECT COUNT(*) AS TOTAL FROM ASIGNATURA
  ) cnt_avg,
  CAR
FROM ASIGNATURA
GROUP BY CAR;

使用SCOTT模式中的标准EMP表

演示：

SQL> SELECT COUNT(deptno)
  2    ||'/'
  3    ||
  4    (SELECT COUNT(*) AS TOTAL FROM emp
  5    ) cnt_avg,
  6    deptno
  7  FROM emp
  8  GROUP BY deptno;

CNT_AV     DEPTNO
------ ----------
6/14           30
5/14           20
3/14           10

Answer 2

可能会有效

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