在同一SQL Server查询中使用COUNT和DISTINCT

Question

我有一个SQL Server表 Cascading ，结构如下：

+----+--------+----------------+           +----------------+-----------+  
| ID | NodeID | ActivationTime |           | ActivationTime | NodeCount |  
+----+--------+----------------+           +----------------+-----------+  
| 1  | 448    | 1              |           | 1              | 1         |  
| 2  | 195    | 2              |           | 2              | 3         |  
| 3  | 504    | 2              |           | 3              | 6         |  
| 4  | 609    | 2              |           | ...            | ...       |  
| 5  | 15     | 3              |           | ...            | ...       |  
| 6  | 31     | 3              |    =>     | ...            | ...       |  
| 7  | 56     | 3              |           | ...            | ...       |  
| 8  | 461    | 3              |           | ...            | ...       |  
| 9  | 585    | 3              |           | ...            | ...       |  
| 10 | 345    | 3              |           | ...            | ...       |  
| .. | ...    | ...            |           | ...            | ...       |  
+----+--------+----------------+           +----------------+-----------+

我需要计算NodeID出现在具有DISTINCT ActivationTime的表中的次数。例如，ActivationTime 1处有1个节点，ActivationTime 2处有3个节点，ActivationTime 3处有6个节点，依此类推。所需的结果显示在右侧。

我尝试了以下不成功的查询：

SELECT DISTINCT(ActivationTime) FROM CASCADING WHERE ActivationTIme IN
(SELECT DISTINCT(COUNT(ActivationTime)) AS NodeCount FROM CASCADING
GROUP BY ActivationTime)

Answer 1

使用COUNT（DISTINCT NodeID）和GROUP BY ActivationTime

{{1}}

Answer 2

SELECT COUNT（NodeCount）AS Count，ActivationTime FROM CASCADING GROUP BY ActivationTime

Answer 3

通过以下方式对我有用：

select activationtime, count(*) from cascading group by activationtime;