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

Question

如您所见，这很糟糕。有什么选择吗？我尝试在 group by 子句中使用列别名，但无济于事。

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：我真的想问如何拥有单个案例源，但无论如何都欢迎案例修改（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，因此某些列出的解决方案对我的用例无效，因为将值排除在间隔之外。

教训：

如果可能且值得，在 case 表达式中寻找模式以减少它

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

使用内联视图来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（到目前为止没有例子:-)）

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，因为很多人都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:-)，很抱歉造成混淆）。

score 9 · Accepted Answer

你有什么理由不使用between吗？案例陈述本身看起来还不错。如果你真的讨厌它，你可以把所有这些都扔到一个表中并映射它。

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

ETC...

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

编辑：或者，在使用浮点数并between变得麻烦的情况下。

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

score 9 · Accepted Answer

问：如何获取别名以在 GROUP BY 子句中使用

一种方法是使用内联视图。[编辑] Remus Rusanu (+1!) 的回答给出了一个通用表表达式的例子来完成同样的事情。[/编辑]

内联视图为您提供复杂表达式的简单“别名”，然后您可以在外部查询的 GROUP BY 子句中引用它：

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

让我们打开它。

调用内部（缩进）查询和内联视图（我们给它一个别名d）
在外部查询中，我们可以duration从d

这应该足以回答你的问题。如果您正在寻找等效的替换表达式，来自tekBlues ( +1 ! ) 的表达式是正确的答案（它适用于边界和非整数。）

使用来自 tekBlues (+1!) 的替换表达式：

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

（这应该足以回答您的问题。）

[更新：] 示例用户定义函数（内联 CASE 表达式的替代品）

CREATE FUNCTION [dev].[udf_duration](@cd FLOAT)
RETURNS SMALLINT
AS
BEGIN
  DECLARE @bucket SMALLINT
  SET @bucket = 
  CASE
  WHEN @cd >= 600 THEN 12
  WHEN @cd >= 540 THEN 11
  WHEN @cd >= 480 THEN 10
  WHEN @cd >= 420 THEN 9
  WHEN @cd >= 360 THEN 8
  WHEN @cd >= 300 THEN 7
  WHEN @cd >= 240 THEN 6
  WHEN @cd >= 180 THEN 5
  WHEN @cd >= 120 THEN 4
  WHEN @cd >=  60 THEN 3
  WHEN @cd >=  30 THEN 2
  WHEN @cd >    0 THEN 1
  --ELSE NULL
  END
  RETURN @bucket
END

select count(callid)
     , [dev].[udf_duration](callDuration)
  from callmetatbl
 where programid = 1001
   and callDuration > 0
 group by [dev].[udf_duration](callDuration)

注意：请注意，用户定义的函数会增加开销，并且（当然）会增加对另一个数据库对象的依赖。

此示例函数等效于原始表达式。OP CASE 表达式没有任何间隙，但它确实引用了每个“断点”两次，我更喜欢只测试下限。（CASE 在满足条件时返回。反向进行测试会让未处理的情况（<=0 或 NULL）在没有测试的情况下通过，anELSE NULL不是必需的，但可以添加以确保完整性。

额外细节

（请务必检查性能和优化器计划，以确保它与原始版本相同（或不明显差于）。过去，我在将谓词推入内联视图时遇到问题，看起来不像就像在您的情况下这将是一个问题。）

存储视图

请注意，内联视图也可以作为视图定义存储在数据库中。但是没有理由这样做，除了从你的陈述中“隐藏”复杂的表达式。

简化复杂表达式

使复杂表达式“更简单”的另一种方法是使用用户定义的函数。但是用户定义的函数有其自身的一系列问题（包括性能下降。）

添加数据库“查找”表

一些答案建议向数据库添加“查找”表。我不认为这真的有必要。它当然可以完成，如果您希望能够即时为durationfrom派生不同的值，而不必修改查询并且不必运行任何 DDL 语句（例如，更改视图定义，或修改用户定义的函数）。 callDuration

通过连接到“查找”表，一个好处是您可以通过对“查找”表执行 DML 操作来使查询返回不同的结果集。

但同样的优势实际上也可能是一个缺点。

仔细考虑好处是否真的超过了坏处。考虑新表对单元测试的影响，如何验证查找表的内容是否有效且未更改（任何重叠？是否有任何差距？），对代码持续维护的影响（由于额外的复杂性）。

一些大的假设

这里给出的很多答案似乎都假设这callDuration是一个 INTEGER 数据类型。似乎他们忽略了它不是整数的可能性，但也许我错过了问题中的那个金块。

这是一个相当简单的测试用例来证明：

callDuration BETWEEN 0 AND 30

不等于_

callDuration > 0 AND callDuration < 30

score 5 · Accepted Answer

案例可以这样写：

case 
when callduration >=30 and callduration<600 then floor(callduration/60)+2
when callduration>0 and callduration< 30 then 1 
when callduration>=600 then 12
end

不需要，将其替换为“where callduration>0”

我喜欢之前给出的翻译表答案！这是最好的解决方案

score 4 · Accepted Answer

您需要将 CASE 向下推到查询树的下方，以便 GROUP BY 可以看到它的投影。这可以通过两种方式实现：

使用派生表（Spencer、Adam 和 Jeremy 已经展示了如何使用）

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 >= 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 )
   select count(callid), duration
   from duration_case
   group by duration

两种解决方案在各个方面都是等效的。我发现 CTE 更具可读性，有些人更喜欢派生表，因为它更便携。

score 2 · Accepted Answer

除以callDuration60：

case
        when callDuration between 1 AND 29 then 1
        when callDuration > 600 then 12
        else (callDuration /60) + 2  end
end as duration

请注意，这between包括边界，我假设 callDuration 将被视为整数。

更新：
将此与其他一些答案结合起来，您可以将整个查询归结为：

select count(d.callid), d.duration
from (   
       select callid
            , case
                when callDuration between 1 AND 29 then 1
                when callDuration > 600 then 12
                else (callDuration /60) + 2  end
              end as duration
        from callmetatbl
        where programid = 1001
              and callDuration > 0
    ) d
group by d.duration

score 1 · Accepted Answer

select count(callid), duration from
(
    select 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
) source
group by duration

score 1 · Accepted Answer

未经测试：

select  count(callid) , duracion
from
    (select 
        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        
            else 0
        end as duracion
    from callmetatbl
    where programid = 1001) GRP
where duracion > 0
group by duracion

score 1 · Accepted Answer

将所有案例添加到表变量中并进行外连接

DECLARE @t TABLE(durationFrom INT, durationTo INT, result INT)
--        when callDuration > 0 and callDuration < 30 then 1
INSERT INTO @t VALUES(1, 30, 1);
--        when callDuration >= 30 and callDuration < 60 then 2
INSERT INTO @t VALUES(30, 60, 2);

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

score 1 · Accepted Answer

这是我的镜头。您需要的所有组件都可以在直接 SQL 中完成。

select
  count(1) as total
 ,(fixedDuration / divisor) + adder as duration
from
(
    select
      case/*(30s_increments_else_60s)*/when(callDuration<60)then(120)else(60)end as divisor
     ,case/*(increment_by_1_else_2)*/when(callDuration<30)then(1)else(2)end as adder
     ,(/*duration_capped@600*/callDuration+600-ABS(callDuration-600))/2 as fixedDuration
     ,callDuration
    from 
      callmetatbl
    where
      programid = 1001
    and 
      callDuration > 0
) as foo
group by
  (fixedDuration / divisor) + adder

这是我用于测试的 SQL。（我没有自己的私人电话metatbl ;）

select
  count(1) as total
 ,(fixedDuration / divisor) + adder as duration
from
(
    select
      case/*(30s_increments_else_60s)*/when(callDuration<60)then(120)else(60)end as divisor
     ,case/*(increment_by_1_else_2)*/when(callDuration<30)then(1)else(2)end as adder
     ,(/*duration_capped@600*/callDuration+600-ABS(callDuration-600))/2 as fixedDuration
     ,callDuration
    from -- callmetatbl -- using test view below
      (  
       select 1001 as programid,   0 as callDuration union
       select 1001 as programid,   1 as callDuration union
       select 1001 as programid,  29 as callDuration union
       select 1001 as programid,  30 as callDuration union
       select 1001 as programid,  59 as callDuration union
       select 1001 as programid,  60 as callDuration union
       select 1001 as programid, 119 as callDuration union
       select 1001 as programid, 120 as callDuration union
       select 1001 as programid, 179 as callDuration union
       select 1001 as programid, 180 as callDuration union
       select 1001 as programid, 239 as callDuration union
       select 1001 as programid, 240 as callDuration union
       select 1001 as programid, 299 as callDuration union
       select 1001 as programid, 300 as callDuration union
       select 1001 as programid, 359 as callDuration union
       select 1001 as programid, 360 as callDuration union
       select 1001 as programid, 419 as callDuration union
       select 1001 as programid, 420 as callDuration union
       select 1001 as programid, 479 as callDuration union
       select 1001 as programid, 480 as callDuration union
       select 1001 as programid, 539 as callDuration union
       select 1001 as programid, 540 as callDuration union
       select 1001 as programid, 599 as callDuration union
       select 1001 as programid, 600 as callDuration union
       select 1001 as programid,1000 as callDuration
      ) as callmetatbl
    where
      programid = 1001
    and 
      callDuration > 0
) as foo
group by
  (fixedDuration / divisor) + adder

SQL 输出如下所示，每个持续时间（存储桶）从 1 到 12 计算 2 条记录。

total  duration
2             1
2             2
2             3
2             4
2             5
2             6
2             7
2             8
2             9
2            10
2            11
2            12

以下是“foo”子查询的结果：

divisor adder   fixedDuration  callDuration
120         1               1             1
120         1              29            29
120         2              30            30
120         2              59            59
60          2              60            60
60          2             119           119
60          2             120           120
60          2             179           179
60          2             180           180
60          2             239           239
60          2             240           240
60          2             299           299
60          2             300           300
60          2             359           359
60          2             360           360
60          2             419           419
60          2             420           420
60          2             479           479
60          2             480           480
60          2             539           539
60          2             540           540
60          2             599           599
60          2             600           600
60          2             600          1000

干杯。

score 1 · Accepted Answer

这里的用户定义函数有什么问题？您既可以直观地清理代码，也可以通过这种方式集中功能。就性能而言，除非您在所说的 UDF 中做一些真正延迟的事情，否则我看不出这个命中太可怕了。

score 1 · Accepted Answer

为使用查找表创建查找duration
表也会加快SELECT语句的速度。

这是查找表的最终结果。

select  count(a.callid), b.ID as duration
from    callmetatbl a
        inner join DurationMap b 
         on a.callDuration >= b.Minimum
        and a.callDuration < IsNUll(b.Maximum, a.CallDuration + 1)
group by  b.ID

这是查找表。

create table DurationMap (
    ID          int identity(1,1) primary key,
    Minimum     int not null,
    Maximum     int 
)

insert  DurationMap(Minimum, Maximum) select 0,30
insert  DurationMap(Minimum, Maximum) select 30,60
insert  DurationMap(Minimum, Maximum) select 60,120
insert  DurationMap(Minimum, Maximum) select 120,180
insert  DurationMap(Minimum, Maximum) select 180,240
insert  DurationMap(Minimum, Maximum) select 240,300
insert  DurationMap(Minimum, Maximum) select 300,360
insert  DurationMap(Minimum, Maximum) select 360,420
insert  DurationMap(Minimum, Maximum) select 420,480
insert  DurationMap(Minimum, Maximum) select 480,540
insert  DurationMap(Minimum, Maximum) select 540,600
insert  DurationMap(Minimum) select 600

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

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