Sql 子查询返回的值超过1，即使使用IN运算符

我的查询很大，但为了理解，我将其粘贴在这里

SELECT    DISTINCT 
                  ISNULL(CD.InteractionID,'')       AS  InteractionID
                , ISNULL(CD.CaseID,'')                  AS CaseID
                , ISNULL(CD.AnalysisMonth,'')  + '-' + CAST( AnalysisYear AS VARCHAR(10)) AS MonYr
                , ISNULL(ServiceType,'')            AS ServiceType
                , ISNULL(ServiceSubType,'')         AS ServiceSubType  
                , ISNULL(SM.SourceName,'')          AS SourceName
                , ISNULL(UserComment,'')            AS UserComment
                , ISNULL(Final,'')                  AS Final
                , ISNULL(SYSM.SystemName,'')        AS SystemName
                , ISNULL(SSM.SubSystem,'')          AS SubSystem
                , ISNULL(CM.CategoryDesc,'')        AS CategoryDesc
                , ISNULL(ITCM.ITCommentDesc,'')     AS ITCommentDesc
                , ISNULL(Casedetails,'')            AS Casedetails
                , ISNULL(TempRCA,'')                AS TempRCA
                , ISNULL(FinalRCA,'')               AS FinalRCA
                , ISNULL(SysOwnerComments  ,'')     AS SysOwnerComments 
             FROM     
                [IT_COMPLAINTS].[ITC_Casedetails]       CD      WITH (NOLOCK) 
            INNER JOIN  [IT_COMPLAINTS].ITC_SourceMaster        SM      WITH (NOLOCK) ON  CD.SourceID   =SM.SourceID    
            LEFT JOIN   [IT_COMPLAINTS].[ITC_SystemMaster]      SYSM    WITH (NOLOCK) ON  CD.SystemID   =SYSM.SystemID    
            LEFT JOIN   [IT_COMPLAINTS].[ITC_SubSystemMaster]   SSM     WITH (NOLOCK) ON  CD.SubSystemID=SSM.SubSystemID AND CD.SystemID=SSM.SystemID    
            LEFT JOIN   [IT_COMPLAINTS].[ITC_CategoryMaster]    CM      WITH (NOLOCK) ON  CD.CategoryID =CM.CategoryID    
            LEFT JOIN   [IT_COMPLAINTS].[ITC_ITCommentMaster]   ITCM    WITH (NOLOCK) ON  CD.ITCommentID=ITCM.ITCommentID   
            INNER JOIN  [IT_COMPLAINTS].[ITC_SystemUserMapping] MAP WITH (NOLOCK) ON SSM.SubSystemID = MAP.SubSystemID
           WHERE 
                (IsNull(@InteractionNo,'')=''   OR ISNULL(CD.InteractionID,'')=@InteractionNo) 
            AND (ISNULL(@Mon,'' )=''            OR ISNULL(CD.AnalysisMonth,'')=@Mon) 
            AND (IsNull(@Year,0)=0              OR ISNULL(CD.AnalysisYear,'')=@Year) 

--    
            AND CD.SystemID IN 
                 ( CASE WHEN @SystemID = 0 THEN 
                         (SELECT SystemID 
                          FROM IT_COMPLAINTS.ITC_SystemUserMapping 
                          WHERE UserID = @UserID AND IsActive = 1) 
                   ELSE @SystemID END)

            AND CD.SubSystemID IN 
                 (CASE WHEN @SystemID = 0 THEN 
                       (SELECT SubSystemID 
                        FROM IT_COMPLAINTS.ITC_SystemUserMapping 
                        WHERE UserID = @UserID AND IsActive = 1) 
                  WHEN @SystemID > 0 AND @SubSystemID = 0 THEN 
                       (SELECT SubSystemID 
                        FROM IT_COMPLAINTS.ITC_SystemUserMapping 
                        WHERE UserID = @UserID AND 
                              IsActive = 1 AND 
                              SystemID = @SystemID)
                  ELSE @SubSystemID END)
--
            AND (ISNULL(@CategoryID,'')=''      OR ISNULL(CD.CategoryID,'')=@CategoryID) 
            AND (ISNULL(@ITCommentID,0)=0       OR ISNULL(CD.ITCommentID,'')=@ITCommentID)

但是，当我运行这个时，它会给我一个错误

子查询返回了多个值。当子查询在=、！=、=或者当子查询用作表达式时

问题在下一部分

AND CD.SystemID IN 
    ( CASE WHEN @SystemID = 0 THEN 
      (SELECT SystemID 
       FROM IT_COMPLAINTS.ITC_SystemUserMapping 
       WHERE UserID = @UserID AND 
         IsActive = 1) ELSE @SystemID END) 
AND CD.SubSystemID IN 
          (CASE WHEN @SystemID = 0 THEN 
            (SELECT SubSystemID 
             FROM IT_COMPLAINTS.ITC_SystemUserMapping 
             WHERE UserID = @UserID AND 
               IsActive = 1) 
          WHEN @SystemID > 0 AND @SubSystemID = 0 THEN 
           (SELECT SubSystemID 
            FROM IT_COMPLAINTS.ITC_SystemUserMapping 
            WHERE UserID = @UserID AND 
              IsActive = 1 AND 
              SystemID = @SystemID)
          ELSE @SubSystemID END)

---

当我对此进行评论时，我的查询是有效的，但是这里的子查询和Case有什么问题？

就像@zedfoxus评论的一样，问题是这一部分：

。。。然后从IT_COMPLAINTS.ITC_SystemUserMapping中选择SubSystemID

因为如果它返回的值超过1，就没有地方放置该值。您应该将其替换为以下内容：

CD.SubSystemID IN (
    SELECT 
      SubSystemID 
    FROM 
      IT_COMPLAINTS.ITC_SystemUserMapping 
    WHERE 
      UserID = @UserID AND 
      IsActive = 1 AND 
      (
        @SystemID = 0 or 
        (SystemID = @SystemID and @SubSystemID = 0)
      ) 
    union all 
    select @SybSystemID where @SystemID > 0 and @SubSystemID > 0
    )

SELECT
    UserID, SystemID,
    count(*) as "Count",
    min(SubSystemID) as minSubSystemID, max(SubSystemID) as maxSubSystemID)
FROM IT_COMPLAINTS.ITC_SystemUserMapping 
WHERE IsActive = 1
GROUP BY UserID, SystemID
HAVING COUNT(*) > 1

这可能需要做一些小的调整，但你应该明白这一点

---

与此相反，您可能希望研究使用if-exists类型的结构。编写起来通常简单得多，性能也更好。

在下面的WHERE子句中，您似乎会为SubSystemID WITH和SystemID=@SystemID返回多个值：

与此相反：

            FROM     
                [IT_COMPLAINTS].[ITC_Casedetails]  CD  WITH (NOLOCK) 
...    
AND CD.SystemID IN 
    ( CASE WHEN @SystemID = 0 THEN 
      (SELECT SystemID 
       FROM IT_COMPLAINTS.ITC_SystemUserMapping 
       WHERE ...) ELSE @SystemID END) 
AND CD.SubSystemID IN 
          (CASE WHEN @SystemID = 0 THEN 
            (SELECT SubSystemID 
             FROM IT_COMPLAINTS.ITC_SystemUserMapping 
             WHERE ...) 
          WHEN @SystemID > 0 AND @SubSystemID = 0 THEN 
           (SELECT SubSystemID 
            FROM IT_COMPLAINTS.ITC_SystemUserMapping 
            WHERE ...)
          ELSE @SubSystemID END)

考虑CD.SystemID和CD.SubSystemID上的左外部联接表IT_.ITC_SystemUserMapping

比如：

FROM  [IT_COMPLAINTS].[ITC_Casedetails]  CD  WITH (NOLOCK) left outer join
      IT_COMPLAINTS.ITC_SystemUserMapping i on
         CD.SystemID = @SystemID or
         (@SystemID = 0 and 
          CD.SystemID = SystemID and UserID = @UserID AND IsActive = 1 ) and
         CD.SubSystemID = @SubSystemID or
         (CD.SubSystemID = SubSystemID and 
          UserID = @UserID AND IsActive = 1 and 
          (@SystemID = 0 or 
           @SystemID > 0 AND SystemID = @SystemID))

---

您可以通过以下查询识别可能导致问题的用户和系统对：

CD.SubSystemID IN (
    SELECT 
      SubSystemID 
    FROM 
      IT_COMPLAINTS.ITC_SystemUserMapping 
    WHERE 
      UserID = @UserID AND 
      IsActive = 1 AND 
      (
        @SystemID = 0 or 
        (SystemID = @SystemID and @SubSystemID = 0)
      ) 
    union all 
    select @SybSystemID where @SystemID > 0 and @SubSystemID > 0
    )

SELECT
    UserID, SystemID,
    count(*) as "Count",
    min(SubSystemID) as minSubSystemID, max(SubSystemID) as maxSubSystemID)
FROM IT_COMPLAINTS.ITC_SystemUserMapping 
WHERE IsActive = 1
GROUP BY UserID, SystemID
HAVING COUNT(*) > 1

我同意@JamesZ的回答。如果您不喜欢没有from子句的union和查询，我认为您可以在单个查询中完成

SELECT SubSystemID 
FROM IT_COMPLAINTS.ITC_SystemUserMapping 
WHERE
    UserID = @UserID AND IsActive = 1 AND 
    (
            @SystemID = 0
        or  SystemID = @SystemID and @SubSystemID = 0
        --  assumes that there's a row in this table with this SubSystemID
        or  SubSystemID = @SubSystemID
    )    

---

我不认为您可以在内部使用CASE…在这种情况下，您有多个子查询。其中一个正在返回多个值。请用左联接替换该部分。在x=y和..为什么所有的NOLOCK提示都在这里？您对查询中不准确的结果满意吗？这里的where子句中还有很多不可争论的谓词。您似乎有许多列允许NULL，但您必须不断地将其强制为空字符串。这种事情会扼杀您的性能。您应该能够通过注释3条SELECT语句中的2条来进一步缩小问题范围。其中一个或多个正在返回多个值，这些值可能是相同的。在本例中，它将是且SystemID=0