Question

可能重复：
CASE equivalent of a nested IIF statement

我正在尝试将以下Access查询转换为T-SQL，但我遇到了IIF语句问题。

访问查询

SELECT 
qry_LAB_LOAD_Prequery2.Asset AS SITE_REF,
Format([Det],"00000") AS DET_, 
IIf(IsNull([MT]),"0",IIf(Right([SP_Ref],2)="WZ"
And IsNull([LabLoadFileSuffix_MT]) 
And [MT]>0,CStr([MT]) & "CT",CStr([MT]) & [LabLoadFileSuffix_MT])) AS MT_COUNT,  
IIf(IIf(IsNull([MT]),0,[MT])>=IIf(IsNull([IM]),0,[IM]),0,
IIf(IsNull([IM]),"0",IIf(Right([SP_Ref],2)="WZ" 
And IsNull([LabLoadFileSuffix_IM]),CStr([IM]) 
& "CT",CStr([IM]) & [LabLoadFileSuffix_IM]))) AS IM_COUNT,   
qry_LAB_LOAD_Prequery2.[2012 Sample Point] AS SP_REF, qry_LAB_LOAD_Prequery2.Area
FROM qry_LAB_LOAD_Prequery2
WHERE (((IIf(IsNull([IM]),0,[IM])+IIf(IsNull([MT]),0,[MT]))>0));

我试图转换它的一部分。任何人都可以帮我纠正嵌套的IID语句，因为我不确定。

SQL查询

SELECT qry_LAB_LOAD_Prequery2.Asset AS SITE_REF,
RIGHT('00000' + CAST([Det] AS VARCHAR(5)),5) AS DET_,
  ----- (the nested iff statements)
qry_LAB_LOAD_Prequery2.[2012 Sample Point] AS SP_REF,
qry_LAB_LOAD_Prequery2.Area
FROM qry_LAB_LOAD_Prequery2
where (ISNull([IM],0) + ISNULL([MT],0)) > 0

Answer 1

要转换嵌套的IIF，您需要用户CASE。

让我们拿第一个：

重新格式化我得到：

IIf(
          IsNull([MT]),
          "0",
                   IIf(Right([SP_Ref],2)="WZ"
                            And IsNull([LabLoadFileSuffix_MT]) 
                            And [MT]>0,

                        CStr([MT]) & "CT",
                        CStr([MT]) & [LabLoadFileSuffix_MT]
                    )
    ) AS MT_COUNT,

转换为：

CASE
WHEN [MT] IS NULL 
    THEN "0",
ELSE
    CASE 
        WHEN Right([SP_Ref],2) = "WZ"
           AND ([LabLoadFileSuffix_MT] IS NULL
               AND [MT]>0
        THEN 
             CAST([MT] AS VARCHAR) + "CT"
        ELSE
             CAST([MT] AS VARCHAR) + [LabLoadFileSuffix_MT]
    END
END AS MT_COUNT,

简化为：

CASE
WHEN [MT] IS NULL 
    THEN "0",
ELSE
    CAST([MT] AS VARCHAR)  
   + CASE 
        WHEN Right([SP_Ref],2) = "WZ"
           AND ([LabLoadFileSuffix_MT] IS NULL
               AND [MT]>0
        THEN 
             "CT"
        ELSE
             [LabLoadFileSuffix_MT]
    END
END AS MT_COUNT,

对于第二个，我重新格式化，然后将其转换为以下

CASE WHEN 

    CASE 
      WHEN [MT] IS NULL THEN 0 
      ELSE [MT] 
    END 

     >=

    CASE 
      WHEN [IM] IS NULL THEN 0 
      ELSE [IM] 
    END ,

 THEN   0,
 ELSE    

   CASE 
      WHEN [IM] IS NULL THEN "0" 
      ELSE 

        CASE 
          WHEN Right([SP_Ref],2) = "WZ" AND [LabLoadFileSuffix_IM] IS NULL THEN CAST([IM] AS VARCHAR) + "CT"
          ELSE CAST([IM] AS VARCHAR) + [LabLoadFileSuffix_IM]
        END
      END
 END
 AS IM_COUNT,

Whick缩减为

CASE 
      WHEN ISNULL([MT], 0) > =  ISNULL([IM], 0)
 THEN   0,
 ELSE    
   CASE 
      WHEN [IM] IS NULL THEN "0" 
      ELSE 
        CAST([IM] AS VARCHAR) +
        CASE 
          WHEN Right([SP_Ref],2) = "WZ" AND [LabLoadFileSuffix_IM] IS NULL THEN "CT"
          ELSE  [LabLoadFileSuffix_IM]
        END
      END
 END
 AS IM_COUNT,

这两个列基本上归结为两个非常相似的表达式。

Answer 2

尝试嵌套的case语句。

所以只需占用前2行：

IIf(IsNull([MT]),"0",IIf(Right([SP_Ref],2)="WZ"
And IsNull([LabLoadFileSuffix_MT])

会变成

CASE WHEN MT IS NULL 
THEN 0
ELSE
    CASE WHEN RIGHT(SP_Ref, 2) = "WZ" AND LabLoadFileSuffix_MT IS NULL 
    THEN
         ...
    ELSE ...
    END
END

MS-Access查询到T-SQL

2 个答案: