sql-server - 简化(别名)T-SQL CASE 语句。有什么改进的可能吗？

Question

正如你所看到的，这很浪费时间。有什么替代方案吗？我尝试在 group by 子句中使用列别名无济于事。

select count(callid) ,
case
        when callDuration > 0 and callDuration < 30 then 1
        when callDuration >= 30 and callDuration < 60 then 2
        when callDuration >= 60 and callDuration < 120 then 3
        when callDuration >= 120 and callDuration < 180 then 4
        when callDuration >= 180 and callDuration < 240 then 5
        when callDuration >= 240 and callDuration < 300 then 6
        when callDuration >= 300 and callDuration < 360 then 7
        when callDuration >= 360 and callDuration < 420 then 8
        when callDuration >= 420 and callDuration < 480 then 9
        when callDuration >= 480 and callDuration < 540 then 10
        when callDuration >= 540 and callDuration < 600 then 11
        when callDuration >= 600 then 12
end as duration
from callmetatbl
where programid = 1001 and callDuration > 0
group by case
        when callDuration > 0 and callDuration < 30 then 1
        when callDuration >= 30 and callDuration < 60 then 2
        when callDuration >= 60 and callDuration < 120 then 3
        when callDuration >= 120 and callDuration < 180 then 4
        when callDuration >= 180 and callDuration < 240 then 5
        when callDuration >= 240 and callDuration < 300 then 6
        when callDuration >= 300 and callDuration < 360 then 7
        when callDuration >= 360 and callDuration < 420 then 8
        when callDuration >= 420 and callDuration < 480 then 9
        when callDuration >= 480 and callDuration < 540 then 10
        when callDuration >= 540 and callDuration < 600 then 11
        when callDuration >= 600 then 12
end

编辑:
我真的想询问如何拥有单个案例源，但无论如何都欢迎修改案例(尽管不太有用，因为间隔可能会被修改甚至可能会自动生成)。

正如某些人所考虑的那样， callDuration 确实是一个浮点数，因此通过将值排除在间隔之外，某些列出的解决方案对我的用例无效。

类(class):

在 case 表达式中寻找模式以尽可能减少它并且值得

 case
    when callDuration > 0 AND callDuration < 30 then 1
    when callDuration > 600 then 12
    else floor(callDuration/60) + 2  end
 end as duration

使用内联 View 获得案例的单一来源

select count(d.callid), d.duration
from (   
   select callid
        , case
           when callDuration > 0 AND callDuration < 30 then 1
           when callDuration > 600 then 12
           else floor(callDuration/60) + 2  end
          end as duration
    from callmetatbl
    where programid = 1001
          and callDuration > 0
) d
group by d.duration

或者使用公用表表达式

   with duration_case as (
      select callid ,
      case
        when callDuration > 0 AND callDuration < 30 then 1
        when callDuration > 600 then 12
        else floor(callDuration/60) + 2  end
      end as duration
   from callmetatbl
   where programid = 1001 and callDuration > 0 )
    select count(callid), duration
    from duration_case
    group by duration

或者使用用户定义的函数(目前没有示例:-))

或者使用查找表和连接

DECLARE @t TABLE(durationFrom float, durationTo float, result INT)
--populate table with values so the query works
select count(callid) , COALESCE(t.result, 12)
from callmetatbl JOIN @t AS t ON callDuration >= t.durationFrom 
AND callDuration < t.durationTo 
where programid = 1001 and callDuration > 0

感谢大家，我很难选择一个可以接受的答案，因为许多人涵盖了问题的不同部分(我当时认为这是一个简单的问题，答案很简单:-)，抱歉造成困惑)。

Answer 1

您是否有任何理由不使用 between ? case 语句本身看起来还不错。如果你真的讨厌它，你可以把所有这些都扔到一张 table 上并映射出来。

Durations
------------------
low   high   value
0     30     1
31    60     2

等等...

(SELECT value FROM Durations WHERE callDuration BETWEEN low AND high) as Duration

编辑:或者，在使用浮点数和 between 的情况下变得麻烦。

(SELECT value FROM Durations WHERE callDuration >= low AND callDuration <= high) as Duration