sql server 2017中案例条件的意外结果

Question

SELECT CASE WHEN ISNULL(STAFFING_PRIORITY_CODE,'') = 'Billable' AND   
   RESOURCE_TYPE in ('confirmed','provisional')AND PROJECTTYPE IN (select   
   ProjectType from OracleProjectTypeClass WHERE ShortName IN ('FB','TM'))  
   THEN CAST(ISNULL([%_WORK_ALLOCATION],0) AS decimal(18,2))   
   ELSE 0 END as [Billable]From [DBO].BenchDashboard where EMPLOYEE_ID=107500           

  

此查询结果为： -
    计费
    100.00

我们在select语句中再添加一列： -

SELECT CASE WHEN ISNULL(STAFFING_PRIORITY_CODE,'')='Billable'ANDRESOURCE_TYPE in('confirmed','provisional') 
   AND PROJECTTYPE IN (select ProjectType from OracleProjectTypeClass WHERE ShortName IN ('FB','TM'))
   THEN CAST(ISNULL([%_WORK_ALLOCATION],0) AS decimal(18,2)) ELSE 0 END as [Billable]
    --added column
    ,CASE WHEN ISNULL(STAFFING_PRIORITY_CODE,'') = 'Buffer' AND RESOURCE_TYPE in ('confirmed','provisional') 
    AND PROJECTTYPE IN (select ProjectType from OracleProjectTypeClass WHERE ShortName IN ('FB','TM'))
    THEN CAST(ISNULL([%_WORK_ALLOCATION],0) AS decimal(18,2)) ELSE 0 END as [Buffer]From [DBO].BenchDashboard where EMPLOYEE_ID=107500

  

给出结果
    计费|缓冲器
    0.0 | 0.00

第一列（Billable）的数据从100变为0为什么？ 1）此Sql代码在sql server 2008r2或兼容级别100中正常工作 但是在兼容级别140或sql server 2017中出现了问题

  

结果应该是： -
     计费|缓冲器
    100.00 | 0.00

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