嵌套Case语句在SQL查询

Question

我的查询

Declare  @From  DateTime='01 Feb 2013' 
Declare  @To   DateTime='28 Feb 2013 23:59:59' 

Select 
      Case 
        When 
        (
         Select TOP 1 f1.UpdatedOn 
         From TicketTypeFollowUp As f1 with(nolock) 
         Where f1.UpdatedOn<T.UpdatedOn And f1.Ticket=T.Ticket 
         Order By f1.UpdatedOn Desc 
       )IS Null 
        Then Ticket.TicketRaisedOn 

        Else 
        (
         Select TOP 1 f1.UpdatedOn 
         From TicketTypeFollowUp As f1 with(nolock) 
         Where f1.UpdatedOn<T.UpdatedOn And f1.Ticket=T.Ticket 
         Order By f1.UpdatedOn Desc 
       ) End [Start Date] 

     From dbo.TicketTypeFollowUp T with(nolock) 
     --Some Tables Omitted   
     Where CAST(TicketRaisedOn As Date)Between ''+Convert(VarChar(19), @From, 100)+''  And ''+Convert(VarChar(19), @To, 100)+'' 

如果列[Start Date]具有值大于@To然后@To值应打印否则[开始日期]列

我怎样才能把它写在相同的查询？

我想什么

 Case When(
      Case 
        When 
        (
         Select TOP 1 f1.UpdatedOn 
         From TicketTypeFollowUp As f1 with(nolock) 
         Where f1.UpdatedOn<T.UpdatedOn And f1.Ticket=T.Ticket 
         Order By f1.UpdatedOn Desc 
       )IS Null 
        Then Ticket.TicketRaisedOn 

        Else 
        (
         Select TOP 1 f1.UpdatedOn 
         From TicketTypeFollowUp As f1 with(nolock) 
         Where f1.UpdatedOn<T.UpdatedOn And f1.Ticket=T.Ticket 
         Order By f1.UpdatedOn Desc 
       ) End [Start Date] 
      )> @To Then @To Else [Start Date] End, 

DB：SQL SERVER 2008

Answer 1

它看起来对我来说，你需要这样的：

Declare  @From  DateTime='01 Feb 2013' 
Declare  @To   DateTime='28 Feb 2013 23:59:59' 

Select CASE WHEN ISNULL(StartDates.[Start Date], Ticket.TicketRaisedOn) > @To THEN @To ELSE ISNULL(StartDates.[Start Date], Ticket.TicketRaisedOn) END AS ResultValue 
From dbo.TicketTypeFollowUp T with(nolock) 
    --Some Tables Omitted 
    OUTER APPLY 
    (
     Select TOP 1 f1.UpdatedOn AS [Start Date] 
     From TicketTypeFollowUp As f1 with(nolock) 
     Where f1.UpdatedOn<T.UpdatedOn And f1.Ticket=T.Ticket 
     Order By f1.UpdatedOn Desc 
    ) StartDates 
Where CAST(TicketRaisedOn As Date)Between ''+Convert(VarChar(19), @From, 100)+''  And ''+Convert(VarChar(19), @To, 100)+'' 

外应用用于指定每行一个计算值，从上面的连接表中引用值，但在那之后它就像来自JOIN的数据。所以你给你的APPLY一个别名，就像它是一个表一样，然后根据需要多次访问它的值。

正如你所看到的，这大大简化了您的query--适用是非常方便的在你的工具带。）））

编辑新增根据注释另一ISNULL。