为什么使用 CASE 语句会得到不同的结果？答案

【问题标题】：Why do I have different result by using CASE statement?为什么使用 CASE 语句会得到不同的结果？
【发布时间】：2016-06-15 00:32:05
【问题描述】：

我正在使用 CASE 语句来计算溢价，如果我只使用 SELECT SUM 语句，结果会很差。为什么会这样？

select 
        SUM(CASE WHEN Premium > 0 and Premium <= 5000 AND Year(EffectiveDate)=2016 AND PolicyType = 'New Business' THEN Premium ELSE 0 END) as '0-5K_WP',
        SUM(CASE WHEN Premium > 5000 and Premium <=10000 AND Year(EffectiveDate)=2016 AND PolicyType = 'New Business' THEN Premium ELSE 0 END) AS '5K-10K_WP',
        SUM(CASE WHEN Premium > 10000 and Premium <= 25000 AND Year(EffectiveDate)=2016 AND PolicyType = 'New Business'   THEN Premium ELSE 0 END) AS '10K-25K_WP',
        SUM(CASE WHEN Premium > 25000 and Premium <=50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'New Business'  THEN Premium ELSE 0 END) AS '25K-50K_WP',
        SUM(CASE WHEN Premium > 50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'New Business'  THEN Premium ELSE 0 END) AS '>50K_WP'
FROM    Test_Plaza_ProductionReport 

union all 
select 
        SUM(CASE WHEN Premium > 0 and Premium <= 5000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) as '0-5K_WP',
        SUM(CASE WHEN Premium > 5000 and Premium <=10000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '5K-10K_WP',
        SUM(CASE WHEN Premium > 10000 and Premium <= 25000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '10K-25K_WP',
        SUM(CASE WHEN Premium > 25000 and Premium <=50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '25K-50K_WP',
        SUM(CASE WHEN Premium > 50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '>50K_WP'
FROM    Test_Plaza_ProductionReport 

union all 
select 

        SUM(CASE WHEN Premium >0 and Premium <= 5000 AND Year(EffectiveDate)=2016 AND  PolicyType = 'Rewrite' THEN Premium ELSE 0 END) as '0-5K_WP',
        SUM(CASE WHEN Premium > 5000 and Premium <=10000 AND Year(EffectiveDate)=2016 AND  PolicyType = 'Rewrite' THEN Premium ELSE 0 END) AS '5K-10K_WP',
        SUM(CASE WHEN Premium > 10000 and Premium <= 25000 AND Year(EffectiveDate)=2016 AND  PolicyType = 'Rewrite' THEN Premium ELSE 0 END) AS '10K-25K_WP',
        SUM(CASE WHEN Premium > 25000 and Premium <=50000 AND Year(EffectiveDate)=2016 AND  PolicyType = 'Rewrite' THEN Premium ELSE 0 END) AS '25K-50K_WP',
        SUM(CASE WHEN Premium > 50000 AND Year(EffectiveDate)=2016 AND  PolicyType = 'Rewrite' THEN Premium ELSE 0 END) AS '>50K_WP'
FROM    Test_Plaza_ProductionReport

总和将是 13,286,473 但现在如果我使用这个：

select sum(premium) 
from Test_Plaza_ProductionReport  
where PolicyType in ('New Business','Renewal','Rewrite') 
and Year(EffectiveDate)=2016

现在总和是 11,993,445 减200万！！这怎么可能？

【问题讨论】：

在标准中看不到任何重叠，但您在基础数据中有负值
约翰，是的，我确实有负值。我也必须考虑到它们。
那么我应该使用什么来考虑它们？
为负值添加一个层。我也会考虑 t tier table 让生活更轻松
旁白：由于 PolicyType 和 year 逻辑并且对于单个 case 中的所有表达式都是通用的 select 您可以将其从表达式中删除并添加 where 子句： select ... from Test_Plaza_Production where PolicyType = 'New Business' and Year( EffectiveDate ) = 2016 union ....

标签： sql-server tsql reporting-services

【解决方案1】：

您的保单记录中似乎有一些保费为负数的记录。向简短查询添加条件以拒绝此类负溢价记录应该使您的数字匹配。

如果您想考虑负溢价，请为它们添加一个额外的“桶”，即

select 
        SUM(CASE WHEN Premium < 0 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) as 'Negative_WP',
        SUM(CASE WHEN Premium > 0 and Premium <= 5000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) as '0-5K_WP',
        SUM(CASE WHEN Premium > 5000 and Premium <=10000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '5K-10K_WP',
        SUM(CASE WHEN Premium > 10000 and Premium <= 25000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '10K-25K_WP',
        SUM(CASE WHEN Premium > 25000 and Premium <=50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '25K-50K_WP',
        SUM(CASE WHEN Premium > 50000 AND Year(EffectiveDate)=2016 AND PolicyType = 'Renewal' THEN Premium ELSE 0 END) AS '>50K_WP'
FROM    Test_Plaza_ProductionReport

【讨论】：

哦，你是对的。我确实有负保费，但我也必须考虑到它们。
是的！！！！非常感谢你！我只是想知道，如果我不将它放入单独的“桶”中，为什么它不会给我相同的结果？说 SUM(CASE WHEN Premium
@Oleg Premium < 0 and Premium <= 5000 是多余的：如果某个值小于零，那么它肯定也小于 5000。不过，使用 Premium <= 5000 会起作用。
谢谢哥们。很抱歉提出愚蠢的问题。我想我该回家了

【解决方案2】：

您很可能有一个负数，但您的 CASE 语句仅适用于正数。

运行相同的查询，最后一个 sum 加上额外的 where 谓词，用于检查 premium

【讨论】：

【解决方案3】：

供您考虑，正如我所提到的，这是使用层表的一种方法。想象一下，定义的多个层支持大量请求和报告

假设您有一个这样的表 Tiers

Tier_Grp      Tier_Title    Tier_R1         Tier_R2
Policy Size   < 0           -999999999.00   0.00
Policy Size   0 - 5K         0.00           5000.00
Policy Size   5K - 10K       5000.00        10000.00
Policy Size   10K - 25K      10000.00       25000.00
Policy Size   25K - 50K      25000.00       50000.00
Policy Size   > 50K          50000.00       999999999.00
Policy Size   Total          -999999999.00  999999999.00

然后通过 1 个简单的查询，您可以获得所有数据、计数、总和、平均值

Select PolicyType
      ,B.Tier_Title
      ,NbrOfPolicies = count(*)
      ,Premium       = sum(Policy)
FROM   Test_Plaza_ProductionReport  A
Join   Tiers on (B.Tier_Grp='Policy Size' and Premium between B.Tier_R1 and B.Tier_R2 and Premium<B.Tier_R2)
Where  Year(EffectiveDate)=2016
Group  By PolicyType
      ,B.Tier_Title  
Order  By PolicyType
      ,B.Tier_R2

【讨论】：