SQL Server - как использовать производную таблицу для вычисляемого поля?

Question

Я пытаюсь использовать вычисленное значение поля в предложении WHERE в своем запросе, и после некоторых исследований я знаю, что мне нужно создать производную таблицу. Однако я не уверен в синтаксисе, поскольку мое вычисляемое поле использует оператор CASE, например:

        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,

Я хочу затем использовать значение TaskItemAge в предложении where что-то вроде:

WHERE TaskItemAge > @TaskAgeStart AND TaskItemAge < @TaskAgeEnd

Как поместить этот оператор CASE в суб-выбор?

** * ** * ** * ** * ** РЕДАКТИРОВАТЬ ** * ** * ** * ** * Извините, я все еще немного озадачен тем, как это будет работать. Вот большой фрагмент моего запроса:

    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

Answer 1

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

Answer 2

Andomar - это правильная форма (+1), вот ваш конкретный синтаксис:

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

Answer 3

Также вы можете использовать CTE

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