为什么UNPIVOT在兼容级别80 DB上工作？

我正在尝试在兼容级别80上运行的SQL Server 2008 SP3数据库上使用UNPIVOT提取数据。这应该意味着UNPIVOT无法正常工作，但在某些情况下，它确实可以正常工作...

作品：

形式的独立SELECT查询：

SELECT...FROM...UNPIVOT...WHERE...GROUP BY

不起作用：

同一查询，位于LEFT JOIN ()同一服务器内不同数据库的其他表上。全部处于兼容级别80。

我收到通常的错误消息：

Msg 325, Level 15, State 1, Line 165
Incorrect syntax near 'UNPIVOT'. You may need to set the compatibility level
of the current database to a higher value to enable this feature. See help for
the SET COMPATIBILITY_LEVEL option of ALTER DATABASE.

UNPIVOT解决方法似乎很麻烦，如果可能的话，我希望此查询是独立的且可刷新的。如果可以让查询独立运行，这似乎是合乎逻辑的，那么应该可以在中使用它JOIN。

问题：

为什么有时会起作用？

在这种情况下，如何在中实现UNPIVOT子查询JOIN？

取消子查询：（按要求...）

SELECT 
    YEAR(CAST('1-'+UnPiv.[Date] AS DATE)) "Year",
    MONTH(CAST('1-'+UnPiv.[Date] AS DATE)) "Month",
    CASE [Channel_Org]
        WHEN 'TPR' THEN 'ERP'
        ELSE [Channel_Org]
    END AS [Channel_Org],
    ISNULL(SUM(CASE WHEN [GL Desc] = 'EIP' AND 
        [OPEX_Group] = 'Postpaid SAC' THEN [Amount] END),0) "Post EIP",
    ISNULL(SUM(CASE WHEN [GL Desc] = 'EIP' AND
        [OPEX_Group] = 'Prepaid SAC' THEN [Amount] END),0) "Pre EIP",
    ISNULL(SUM(CASE WHEN [GL Desc] = 'EIP' AND
        [OPEX_Group] = 'SRC' THEN [Amount] END),0) "Upg EIP",
    ISNULL(SUM(CASE WHEN [GL Desc] = 'MDF (OEM)' AND
        [OPEX_Group] = 'Postpaid SAC' THEN [Amount] END),0) "Post MDF",
    ISNULL(SUM(CASE WHEN [GL Desc] = 'MDF (OEM)' AND
        [OPEX_Group] = 'Prepaid SAC' THEN [Amount] END),0) "Pre MDF",
    ISNULL(SUM(CASE WHEN [GL Desc] = 'MDF (OEM)' AND
        [OPEX_Group] = 'SRC' THEN [Amount] END),0) "Upg MDF"
FROM [Channel_Steering].[dbo].[AQ1_OPEX_View]
UNPIVOT (Amount FOR [Date] IN ( [Jan-14],
                                [Feb-14],
                                [Mar-14],
                                [Apr-14],
                                [May-14],
                                [Jun-14],
                                [Jul-14],
                                [Aug-14],
                                [Sep-14],
                                [Oct-14],
                                [Nov-14],
                                [Dec-14])) UnPiv
WHERE   (   [Channel_Org] IN ('Retail','TPR')
                AND
            [GL Desc] IN ('MDF (OEM)', 'EIP')
        )
GROUP BY
    [Channel_Org],
    YEAR(CAST('1-'+UnPiv.[Date] AS DATE)),
    MONTH(CAST('1-'+UnPiv.[Date] AS DATE))

答案在错误消息中：

您可能需要将当前数据库的兼容性级别设置为更高的值才能启用此功能。

“当前数据库”是指上下文数据库，即在其中执行查询的数据库，该数据库不一定与查询中引用的数据库相同。例如，以下生成错误消息：

USE AdventureWorks;
GO
ALTER DATABASE AdventureWorks 
SET COMPATIBILITY_LEVEL = 80;
GO
SELECT
    U.SystemInformationID,
    U.[Database Version],
    U.ColumnName,
    U.Value
FROM AdventureWorks.dbo.AWBuildVersion AS ABV
UNPIVOT 
(
    Value 
    FOR ColumnName IN 
        (
        VersionDate,
        ModifiedDate
        )
) AS U;

以下命令成功执行（假设tempdb兼容性级别> 80）：

USE AdventureWorks;
GO
ALTER DATABASE AdventureWorks 
SET COMPATIBILITY_LEVEL = 80;
GO
USE tempdb; -- Context database
GO
SELECT
    U.SystemInformationID,
    U.[Database Version],
    U.ColumnName,
    U.Value
FROM AdventureWorks.dbo.AWBuildVersion AS ABV -- Still references data in AW DB
UNPIVOT 
(
    Value 
    FOR ColumnName IN 
        (
        VersionDate,
        ModifiedDate
        )
) AS U;

您需要检查产生错误的连接的上下文数据库是什么。