Question

我有以下T-SQL查询，我想在日期的每个小时选择系统21的计数：

Select DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0) [Date],
Case when System= 21 then Count(CurUSSDCnt) else 0 end as Sys21
from table
group by DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0) ,System
order by [Date];

输出将返回如下内容：

Date                    Sys21
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 3552
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 00:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 0
2015-06-29 01:00:00.000 1880
2015-06-29 01:00:00.000 0

而不是：

Date                    Sys21
2015-06-29 00:00:00.000 3552
2015-06-29 01:00:00.000 1880

Answer 1

如果您只需要有关系统21的信息，则需要WHERE子句，而不是CASE表达式：

Select DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0) [Date],
 Count(CurUSSDCnt) as Sys21
from table
where System= 21
group by DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0)
order by [Date];

如果您需要更多系统，请使用ughai's answer中显示的手动数据透视或使用PIVOT：

select TimeHour,[21] as Sys21,[22] as Sys22
from
   (select System,
           DATEADD(hour,DATEDIFF(hour,0,TimeStamp),0) as TimeHour,
           CurUSSDCnt
    from table
    ) t
       PIVOT (COUNT(CurUSSDCnt) for System in ([21],[22])) u

（如果PIVOT列表不是详尽无遗的，您可能需要在子选择中添加WHERE子句：

   (select System,
           DATEADD(hour,DATEDIFF(hour,0,TimeStamp),0) as TimeHour,
           CurUSSDCnt
    from table
    where System in (21,22)) t

）

Answer 2

您应该将count放在CASE之外。即使System= 21记录不存在，也会显示所有小时数。我还将COUNT更改为SUM。

Select DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0) [Date],
SUM(Case when System= 21 then CurUSSDCnt else 0 end) as Sys21
from table
group by DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0)
order by DATEADD (HOUR,DATEDIFF (HOUR,0,TimeStamp),0);

如果您只想要System= 21的那些小时，请使用Damien_The_UnBeliever建议的WHERE条款

T-SQL Group by DateTime

2 个答案: