SQL Server多表别名优先级>缺少列别名

Question

遍历更多“混淆的”代码并进行重构以供理解。以为这是直截了当的，直到我打了第三份案子。我可以假定带引号的列引用的是t_g3视图吗？

原始的FROM部分在下面发布。

FROM  
    [GCCC_ProjectServer_Reporting].dbo.MSP_EpmProject_UserView AS p
INNER JOIN 
    (SELECT 
         t_g3.ProjectUID as ProjectUID
                 ,CASE WHEN @vLastBaseline = 'BL1' AND t_g3.TaskBaseline1StartDate IS NOT NULL THEN t_g3.TaskBaseline1StartDate
                          WHEN @vLastBaseline = 'BL1' AND t_g3.TaskBaseline1StartDate IS NULL THEN t_g3.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL2' AND t_g3.TaskBaseline2StartDate IS NOT NULL THEN t_g3.TaskBaseline2StartDate
                          WHEN @vLastBaseline = 'BL2' AND t_g3.TaskBaseline2StartDate IS NULL THEN t_g3.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL3' AND t_g3.TaskBaseline3StartDate IS NOT NULL THEN t_g3.TaskBaseline3StartDate
                          WHEN @vLastBaseline = 'BL3' AND t_g3.TaskBaseline3StartDate IS NULL THEN t_g3.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL4' AND t_g3.TaskBaseline4StartDate IS NOT NULL THEN t_g3.TaskBaseline4StartDate
                          WHEN @vLastBaseline = 'BL4' AND t_g3.TaskBaseline4StartDate IS NULL THEN t_g3.TaskBaseline5StartDate     
                          ELSE t_g3.TaskBaseline1StartDate          
                 END AS g3_LastBaseline     
                 ,CASE WHEN @vLastBaseline = 'BL1' AND t_cs.TaskBaseline1StartDate IS NOT NULL THEN t_cs.TaskBaseline1StartDate
                          WHEN @vLastBaseline = 'BL1' AND t_cs.TaskBaseline1StartDate IS NULL THEN t_cs.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL2' AND t_cs.TaskBaseline2StartDate IS NOT NULL THEN t_cs.TaskBaseline2StartDate
                          WHEN @vLastBaseline = 'BL2' AND t_cs.TaskBaseline2StartDate IS NULL THEN t_cs.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL3' AND t_cs.TaskBaseline3StartDate IS NOT NULL THEN t_cs.TaskBaseline3StartDate
                          WHEN @vLastBaseline = 'BL3' AND t_cs.TaskBaseline3StartDate IS NULL THEN t_cs.TaskBaseline5StartDate
                          WHEN @vLastBaseline = 'BL4' AND t_cs.TaskBaseline4StartDate IS NOT NULL THEN t_cs.TaskBaseline4StartDate
                          WHEN @vLastBaseline = 'BL4' AND t_cs.TaskBaseline4StartDate IS NULL THEN t_cs.TaskBaseline5StartDate
                          ELSE t_cs.TaskBaseline1StartDate                
                 END AS cs_LastBaseline     
                 ,CASE WHEN @vLastBaseline = 'BL1' AND t_g3.TaskBaseline1StartDate IS NOT NULL THEN 'TaskBaseline1StartDate'
                          WHEN @vLastBaseline = 'BL1' AND t_g3.TaskBaseline1StartDate IS NULL THEN 'TaskBaseline5StartDate'
                          WHEN @vLastBaseline = 'BL2' AND t_g3.TaskBaseline2StartDate IS NOT NULL THEN 'TaskBaseline2StartDate'
                          WHEN @vLastBaseline = 'BL2' AND t_g3.TaskBaseline2StartDate IS NULL THEN 'TaskBaseline5StartDate'
                          WHEN @vLastBaseline = 'BL3' AND t_g3.TaskBaseline3StartDate IS NOT NULL THEN 'TaskBaseline3StartDate'
                          WHEN @vLastBaseline = 'BL3' AND t_g3.TaskBaseline3StartDate IS NULL THEN 'TaskBaseline5StartDate'
                          WHEN @vLastBaseline = 'BL4' AND t_g3.TaskBaseline4StartDate IS NOT NULL THEN 'TaskBaseline4StartDate'
                          WHEN @vLastBaseline = 'BL4' AND t_g3.TaskBaseline4StartDate IS NULL THEN 'TaskBaseline5StartDate'
                          ELSE 't_cs.TaskBaseline1StartDate'        
                 END AS LastBaselineSource
              FROM GCCC_ProjectServer_Reporting.dbo.MSP_EpmTask_UserView AS t_g3
                    LEFT JOIN 
                     GCCC_ProjectServer_Reporting.dbo.MSP_EpmTask_UserView AS t_cs
                    ON t_g3.ProjectUID = t_cs.ProjectUID
                    AND t_cs.TaskIsActive = 1
                    AND t_cs.TaskName = 'Construction Start'
              WHERE t_g3.TaskIsActive = 1
              AND t_g3.TaskName = 'Gate 3 Approval'
              ) as BL
        ON p.ProjectUID = BL.ProjectUID

在这里编码

另一个示例，其中单引号用作列别名包装。在整个代码库中非常常见。这就是为什么我认为上述问题与列别名有关。

SELECT    p0.[Project No], 
    p0.ProjectName,
    isnull(p0.Budg_Centre + ' - ' + p0.Budg_CentreName,' - ') as 'BudgetCentre',
    p0.Budg_Centre,p0.Budg_CentreName,
CASE WHEN DATEDIFF(d,p0.ProjectStartDate,p0.ProjectFinishDate) > 40
                THEN 'Scheduled'
                ELSE 'Unscheduled' END as 'Schedule Status',
            CapFor.Forecasting_Month, 
            CapFor.Forecasting_Year, 
            CapFor.FinancialYr, 
            p0.ProjectOwnerName, 

Answer 1

第3种情况与第一种情况重复的逻辑相同，但报告的是第一种情况选择的列作为字符串。

单引号（'）仅是字符串文字定界符 ¹ 。

双引号（"）可用作字符串定界符或用于引用标识符（与[]可以用于引用标识符的方式相同）。应该如何解释它们取决于QUOTED_IDENTIFIER的当前设置。

所以，不要用列引用替换字符串。

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¹ 当我做出如此自信的断言时，我注定会忘记一些极端情况，不是吗。