Question

我正在尝试在MS Access 2010数据库中运行以下查询：

SELECT a.[Level], max(a.dte) AS nextDate, IIf(a.[Type1Date]<a.[Type2Date],"t1","t2") AS Type
FROM (
    select [Level], Type1Date as dte, Type1Date, Type2Date 
    FROM CommunicationTable WHERE ClientNumber=1
    UNION
    select [Level], Type2Date as dte, Type1Date, Type2Date 
    FROM CommunicationTable WHERE ClientNumber = 1
)  AS a
GROUP BY a.[Level];

但是，Access正在给我一个对话框，说明：

You tried to execute a query that does not include the specified  
expression 'IIf(a.[Type1Date]<a.[Type2Date],"t1","t2")' as part  
of an aggregate function.

任何人都可以解释这意味着什么，并告诉我如何修复代码，以便它返回我要求的字段（Level，nextDate，Type）？

Answer 1

使用组查询时，不能在Select语句中包含列，除非它们也在Group By语句中或聚合中。所以你可能想要使用：

GROUP BY a.[Level], IIf(a.[Type1Date]<a.[Type2Date],"t1","t2")

查询不包含指定的函数

1 个答案: