SQL Server - 如何使用派生表計算字段？

我想在我的查詢中的WHERE子句中使用計算的字段值，經過一些研究後，我知道我需要創建派生表。我不知道語法，但是由於我的計算字段使用像一個CASE語句：SQL Server - 如何使用派生表計算字段？

 CASE T.IsReassigned 
     WHEN 1 THEN DATEDIFF(MINUTE, 
        (SELECT top 1 SXAVWFTaskHistory.CreatedWhenUTC from SXAVWFTaskHistory where TaskID = T.TaskID and StatusID = 7 order by TaskHistoryID desc), 
        SYSDATETIMEOFFSET())       
     ELSE 
     CASE Stat.StatusID  
      WHEN 1 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
      WHEN 2 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
      ELSE DATEDIFF(MINUTE,TSK.CreatedWhenUTC, TH.CreatedWhenUTC) 
     END 
    END as TaskItemAge,

我想那麼在使用TaskItemAge值where子句類似：

WHERE TaskItemAge > @TaskAgeStart AND TaskItemAge < @TaskAgeEnd

怎麼辦我把這個CASE語句放入一個子選擇中？

** * ** * ** * ** * ** 編輯 ** * ** * ** * * * * 對不起，我還是有點困惑，這將如何工作。這裏是我的查詢較大片段：

SELECT TSK.TaskID, --0 
    TH.IsLatest, 
    TH.CreatedWhenUTC as TaskHistoryCreationDate, --10 
    TS.Name AS STATE, 
    CASE T.IsReassigned 
     WHEN 1 THEN DATEDIFF(MINUTE, 
        (SELECT top 1 SXAVWFTaskHistory.CreatedWhenUTC from SXAVWFTaskHistory where TaskID = T.TaskID and StatusID = 7 order by TaskHistoryID desc), 
        SYSDATETIMEOFFSET())       
     ELSE 
     CASE Stat.StatusID  
      WHEN 1 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
      WHEN 2 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
      ELSE DATEDIFF(MINUTE,TSK.CreatedWhenUTC, TH.CreatedWhenUTC) 
     END 
    END as TaskItemAge, 
    ctx.ContextTypeName, 
    ctx.ContextDescription, --15 
    TH.TouchedWhenUTC as TaskHistoryModifiedDate 
INTO #ii   
FROM SXAVWFTask TSK 
INNER JOIN SXAVWFTaskHistory TH ON TSK.TaskID = TH.TaskID 
INNER JOIN @PagedTemp T on TH.TaskHistoryID = T.TaskHistoryID 

Where TaskItemAge > @TaskAgeStart AND TaskItemAge < @TaskAgeEnd

來源

2013-02-05 Dustin Kofoed

A * Derived Table *是由SELECT語句生成（即，派生自）的任何一組行。在SQL Server派生表中，也可用於查詢的項目包括1）子查詢，2）CTE和3）視圖。 – RBarryYoung

select * 
from (
     select case ... end as CaseColumn 
     ,  * 
     from YourTable 
     ) as SubQueryAlias 
where CaseColumn between 1 and 2

來源

2013-02-05 22:55:03 Andomar

Andomar的是正確的形式（+1），這裏是你的特定語法：

SELECT * 
FROM (
    SELECT *, 
     CASE T.IsReassigned 
      WHEN 1 THEN DATEDIFF(MINUTE, 
         (SELECT top 1 SXAVWFTaskHistory.CreatedWhenUTC from SXAVWFTaskHistory where TaskID = T.TaskID and StatusID = 7 order by TaskHistoryID desc), 
         SYSDATETIMEOFFSET())       
      ELSE 
      CASE Stat.StatusID  
       WHEN 1 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
       WHEN 2 THEN DATEDIFF(MINUTE,TSK.CreatedWhenUTC, SYSDATETIMEOFFSET()) -- time duration between when task is created(use SXAVWFTask.CreatedWhenUTC) and now 
       ELSE DATEDIFF(MINUTE,TSK.CreatedWhenUTC, TH.CreatedWhenUTC) 
      END 
     END as TaskItemAge 
    FROM BaseTable 
) as DerivedTable 
WHERE TaskItemAge > @TaskAgeStart AND TaskItemAge < @TaskAgeEnd

來源

2013-02-05 22:58:53

您也可以使用CTE

;WITH cte AS 
    (
    SELECT CASE WHEN ... THEN ... END AS TaskItemAge 
    FROM your_table 
    ) 
    SELECT * 
    FROM cte 
    WHERE TaskItemAge > @TaskAgeStart AND TaskItemAge < @TaskAgeEnd

來源

2013-02-05 22:59:02

我upvoted，但我自己的意見是，如果你只打算使用子查詢一次，使用cte是overengineering。 –

SQL Server - 如何使用派生表計算字段？

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