SQL Server子查詢返回了多個值。這當子查詢跟隨不允許=，！=，<, <= , >，> =（即使我使用IN子句）

Question

SELECT Count(*) 
FROM headcount 
WHERE [mso/bu2] = @MSOBU 
     AND [status] = 'billable' 
     AND [location type] = 'offshore' 
     AND [vertical group] = @Vertical 
     AND lob IN(CASE 
        WHEN @LOB = 'dgtl' THEN (SELECT DISTINCT lob 
               FROM lob 
               WHERE category = 'esg') 
        WHEN @LOB = 'nondgtl' THEN (SELECT DISTINCT lob 
               FROM lob 
               WHERE category <> 'esg') 
        WHEN @LOB = '' THEN (SELECT DISTINCT lob 
              FROM headcount) 
        END) 

我陷進這個錯誤，即使我使用IN子句

Answer 1

你需要像這樣

SELECT Count(*) 
FROM headcount 
WHERE [mso/bu2] = @MSOBU 
     AND [status] = 'billable' 
     AND [location type] = 'offshore' 
     AND [vertical group] = @Vertical 
     AND ((@LOB = 'dgtl' 
       AND lob IN (SELECT DISTINCT lob 
          FROM lob 
          WHERE category = 'esg')) 
       OR (@LOB = 'nondgtl' 
        AND lob IN (SELECT DISTINCT lob 
           FROM lob 
           WHERE category <> 'esg')) 
       OR @LOB = '')) 

Answer 2

CASE的操作數WHEN 必須由一個值，而不是多行。

嘗試重寫查詢這樣的：

select COUNT(*) 
    from HeadCount 
    where [MSO/BU2]=@MSOBU and [Status]='billable' 
    and [Location Type]='offshore' and [Vertical Group]= @Vertical 
    and (@LOB='' 
      OR 
     LOB in(
     select distinct lob from LOB 
      where (@LOB='dgtl' and Category ='esg') OR 
       (@LOB='nondgtl' and Category<>'esg') 
       ) 
     ) 

對於@LOB=''，因爲它選擇主表（人數）的所有行無子查詢的需要。