复杂的枢轴

Question

我已经将复杂的模式简化为以下示例

学生们

• StudentID int,Name varchar(50)
• 比尔
• 2,艾米
• 3,贝丝
• 4,斯科特
• 5,史蒂夫

类

• ClassID int,Name varchar(50),Period varchar(50)
• 1,代数,Period1
• 2,地理,时期3
• 3,生物学,期间5
• 4,物理学,Period4
• 5,演讲,期间2
• 6,历史,时期6

和一个交接表

StudentsClasses

• StudentID int,ClassID int
• 1,1
• 1,4
• 1,5
• 2,6
• 3,5
• 3,4
• 3,6
• 4,1
• 4,4
• 5,5
• 5,6

我的目标是列出每个学生按期间顺序列出的所选课程.我有以下选择

SELECT Name,Period1, Period2, Period3, 
    Period4, Period5, Period6  
    FROM (
SELECT _Students.Name AS [NAME],_Classes.Period AS PIVOT_CODE, _Classes.name as [Class] 
FROM _Classes 
    INNER JOIN _StudentsClasses ON _Classes.ClassID=_StudentsClasses.ClassID 
    INNER JOIN _Students ON _StudentsClasses.StudentID=_Students.StudentID
)
    AS data
    PIVOT 
    (  min([Class])  FOR [PIVOT_CODE] IN 
        (Period1, Period2, Period3, 
    Period4, Period5, Period6)
    ) AS pvt

结果如何

Name   Period1   Period2   Period3   Period4   Period5   Period6
------ --------- --------- --------- --------- --------- ----------
Amy    NULL      NULL      NULL      NULL      NULL      History
Beth   NULL      Speech    NULL      Physics   NULL      History
Bill   Algebra   Speech    NULL      Physics   NULL      NULL
Scott  Algebra   NULL      NULL      Physics   NULL      NULL
Steve  NULL      Speech    NULL      NULL      NULL      History

我需要帮助的地方是我需要将所有非空值移向左列,这样就没有空白了.例如,可以重命名列名称

Name   Choice1   Choice2   Choice3   Choice4   Choice5   Choice6
------ --------- --------- --------- --------- --------- ----------
Amy    History
Beth   Speech    Physics   History
Bill   Algebra   Speech    Physics
Scott  Algebra   Physics
Steve  Speech    History

我可以通过选择一个临时表到一个临时表,然后用光标迭代每一行/列,但我想避免这种情况.任何建议都非常感谢.

Answer 1

假设SQL Server 2005(至少),ROW_NUMBER()用于订购选项:

SELECT Name, Choice1, Choice2, Choice3, Choice4, Choice5, Choice6  
FROM (
    SELECT 
        S.Name AS [NAME], 
        'Choice' + CAST(ROW_NUMBER() OVER(PARTITION BY S.Name ORDER BY S.Name, C.Period) AS VARCHAR) AS PIVOT_CODE, 
         C.Name as [Class]
    FROM Classes C
        JOIN StudentsClasses SC ON C.ClassID = SC.ClassID 
        JOIN Students S ON SC.StudentID = S.StudentID
    )
    AS data
    PIVOT 
    (  min([Class])  FOR [PIVOT_CODE] IN 
        (Choice1, Choice2, Choice3, Choice4, Choice5, Choice6)
    ) AS pvt