SQL Server - 有条件的外部应用

Question

在 SQL Server 2008 中有没有办法做类似下面的事情？

可以根据条件指定外部应用(连接)表吗？

declare @bGetExtendedInfo bit
set @bGetExtendedInfo = 1

declare @param nvarchar(24)
set @param = 'CO-02-BBB'

select t1.*, t2.ID
from t1
outer apply (
              case when @bGetExtendedInfo= 0 
                  then (select 0) as ID  /* dummy value */
                  /*really expensive query trying to avoid when extended info is not needed*/
                  else (select top 1 ID from tbl1 where tbl1.code = @param)
              end
             ) t2

Answer 1

试试这个，

DECLARE @bCond BIT
SET @bCond = 1

SELECT t1.*, t2.*
FROM   t1 OUTER APPLY
             (
                SELECT TOP 1 *
                FROM
                    (
                        SELECT *, 'a' src FROM tb10
                        UNION ALL
                        SELECT *, 'b' src FROM tb11
                    )s
                WHERE   src = CASE WHEN @bCond = 0 THEN 'a' ELSE 'b' END
             ) t2