SQL Server：如何从表中选择其他格式？答案

【问题标题】：SQL Server: How can I SELECT FROM TABLE TO Other Format?SQL Server：如何从表中选择其他格式？
【发布时间】：2010-03-23 16:04:49
【问题描述】：

我有表 A。如何从表 A 中选择表 B 格式？

Table A

Employee Name Effective Date FieldType     FieldValue
Maung Mya           1/1/2005 Title         Project Engineer
Maung Mya           1/1/2005 Department    IT Department
Maung Mya           1/1/2007 Title         Assist Project Manager
Kyaw Kyaw           1/1/2006 Title         Software Engineer
Kyaw Kyaw           1/1/2006 Department    IT Department

Table B

Effective Date Employee Name Title                  Department
1/1/2007       Maung Mya     Assist Project Manager IT Department
1/1/2006       Kyaw Kyaw     Software Engineer      IT Department

【问题讨论】：

标签： sql-server-2005 select

【解决方案1】：

看起来你想要这样的东西：

SELECT A.[Effective Date],
       A.[Employee Name],
       A.FieldValue AS Title,
       A2.FieldValue AS Department
FROM A INNER JOIN
     A AS A2
     ON A.[Employee Name] = A2.[Employee Name] AND
        A.[Effective Date] = A2.[Effective Date] AND
        A.FieldType = 'Title' AND
        A2.FieldType = 'Department'
WHERE A.[Effective Date] = (
    SELECT MAX([Effective Date])
    FROM A AS A3
    WHERE A3.[Employee Name] = A.[Employee Name] AND A3.FieldType = 'Title')
    AND A2.[Effective Date] = (
    SELECT MAX([Effective Date])
    FROM A AS A4
    WHERE A4.[Employee Name] = A2.[Employee Name] AND A3.FieldType = 'Department')

【讨论】：

当我在您的陈述中进行测试时，标题字段在结果中为 NULL。并且第一条记录显示 Maung Mya “项目工程师”而不是“协助项目经理”的第一个标题。
好的，我添加了一个 WHERE 子句，应该会有所帮助。
谢谢，根据您的回答，我得到了我想要检索的答案！

【解决方案2】：

编辑：RedsDevils 我已经编辑了我的代码并使用您的示例对其进行了测试。现在应该可以工作了

考虑到同一名员工可能会更换部门，或通过他的职业生涯获得晋升，我的两个加入者会为每种类型寻找最新生效日期。

SELECT  derived.[Effective Date], 
        derived.[Employee Name],
        title1.[FieldValue] AS Title, 
        dept1.[FieldValue] AS Department
FROM 
    (
        SELECT MAX([Effective Date]) AS [Effective Date], [Employee Name] 
        FROM TableA
        GROUP BY [Employee Name] 
    ) derived

    -- Inner Join for TITLE
    INNER JOIN TableA title1 ON derived.[Employee Name] = title1.[Employee Name]
    AND title1.FieldType = 'Title'
    AND title1.[Effective Date] = (SELECT MAX(title2.[Effective Date]) 
                                FROM TableA title2 
                                WHERE title1.[Employee Name] = title2.[Employee Name] 
                                AND title2.FieldType = 'Title') 

    -- Inner Join for DEPARTMENT
    INNER JOIN TableA dept1 ON derived.[Employee Name] = dept1.[Employee Name]
    AND dept1.FieldType = 'Department'
    AND dept1.[Effective Date] = (SELECT MAX(dept2.[Effective Date]) 
                                FROM TableA dept2 
                                WHERE dept1.[Employee Name] = dept2.[Employee Name] 
                                AND dept2.FieldType = 'Department')

我首先创建了一个派生表来获取 MAX 生效日期和员工姓名，并将其命名为“派生”。然后我创建加入以获得最后知道的Title和Department。

【讨论】：

您的 Statements 结果 10 条记录。我只需要表 B 中的 2 条记录。
抱歉，很匆忙，但我想了解标题和部门的 MAX(effective_date) 原则。如果我有时间吃午饭，我会完全解决它。

【解决方案3】：

是的，我明白了！基于Gabe's answer，我可以检索我想要的格式并且只有2条记录。谢谢大家！答案如下。

SELECT  TableA.[Effective Date],  TableA.[Employee Name],  TableA.FieldValue AS Title,A2.FieldValue AS Department FROM TableA INNER JOIN  TableA AS A2 ON TableA.[EmployeeName] = A2.[EmployeeName] AND  TableA.[EffectiveDate] = (SELECT MAX([EffectiveDate]) FROM TableA AS A3 WHERE A3.[EmployeeName] = TableA.[EmployeeName] AND A3.FieldType = 'Title') AND  TableA.FieldType = 'Title' AND  A2.FieldType = 'Department'

【讨论】：