SQL -带子选择的Group By？

Question

我有以下疑问：

SELECT COUNT(DATEPART(hh, CallStart)), DATEPART(hh, CallStart) as 'Hour'
  FROM PhoneSystemLog 
 WHERE MONTH(CallStart) = @Month and YEAR(CallStart) = @Year 
 GROUP BY DATEPART(hh, CallStart)

这很好，它会将每小时的呼叫数分组，但我想做的是将12am - 7am之间进行的呼叫分组为一组，而将下午6点-12点进行的呼叫分组为一组，因为在这些时间段进行的呼叫并不多，因此在这些时间段内每个小时的呼叫数似乎没有意义(因为他们不在工作时间)。这个是可能的吗？

Answer 1

您可以使用case将小时转换为时段：

select  Period
,       count(*) as Calls
from    (
        select  case 
                when datepart(hh, CallStart) between 0 and 7 then '1-7'
                when datepart(hh, CallStart) between 18 and 23 then '18-24'
                else cast(datepart(hh, CallStart) as varchar(2))
                end as Period
        from    PhoneSystemLog
        where   MONTH(CallStart) = @Month 
                and YEAR(CallStart) = @Year 
        ) as SubQueryAlias
group by
        Period

Answer 2

试试这样的东西

select count(DATEPART(hh, CallStart)), 
    CASE 
    when DATEPART(hh, callstart) between 0 to 7 then '12:00AM-7AM'
    when DATEPART(hh, callstart) between 18 to 23 then '06PM-12AM'
    END
as 'hour' from PhoneSystemLog  
where MONTH(callstart) = @Month and YEAR(callstart) = @Year  
group by 
    CASE 
    when DATEPART(hh, callstart) between 0 to 7 then '12:00AM-7AM'
    when DATEPART(hh, callstart) between 18 to 23 then '06PM-12AM'
    END