如果参数为空，如何使查询条件选择所有内容

Question

我有一个表单，它有一个名为 [Supp] 的组合框，它从名为 [Supplier] 的表列中提取。

同时，我正在过滤与日期范围为 [Text6](Starting Date) 和 [Text7](Ending Date) 的记录关联的日期

我正在尝试使供应商过滤器成为可选，只要您将 [Supp] 留空/空，它就会选择所有供应商。

问题是，每当我将 [Supp] 留空时，它似乎超出了日期范围过滤器并选择所有可用记录，而不管日期如何。我认为这很可能是因为我使用的是“OR”。

SQL Code

SELECT [Table Material Label].Serial, [Table Material Label].[Date Recieved], [Table Material Label].MaterialDescription, [Table Material Label].MaterialCode, [Table Material Label].Supplier, 

[Table Material Label].[Lot Number], [Table Material Label].Weight, [Table Material Label].Quantity, [Table Material Label].[Purchase Order Number], [Table Material Label].[Received By], [Table Material Label].[Checked in By], [Table Material Label].[Total Weight]

FROM [Table Material Label]

WHERE ((([Table Material Label].[Date Recieved])>=[Forms]![Report Generator]![Text6] 
    And ([Table Material Label].[Date Recieved])<=[Forms]![Report Generator]![Text7]) 
    AND (([Table Material Label].Supplier)=IIf([forms]![Report Generator]![Supp].[Value]="*",([Table Material Label].[Supplier])='*',([Table Material Label].[Supplier])=[Forms]![Report Generator]![Supp].[Value])))


ORDER BY [Table Material Label].[Date Recieved], [Table Material Label].MaterialDescription, [Table Material Label].MaterialCode, [Table Material Label].Supplier;

总而言之 - 我正在尝试按日期范围和供应商进行过滤的查询。但如果供应商标准为空白，我希望它不过滤供应商。如果不破坏日期范围过滤器，我将无法执行此操作。

任何帮助将不胜感激。谢谢。

成品，感谢 Andre 的解决方案：

SELECT [Table Material Label].Serial, [Table Material Label].[Date Recieved], [Table Material Label].MaterialDescription, [Table Material Label].MaterialCode, [Table Material Label].Supplier, 

[Table Material Label].[Lot Number], [Table Material Label].Weight, [Table Material Label].Quantity, [Table Material Label].[Purchase Order Number], [Table Material Label].[Received By], [Table Material Label].[Checked in By], [Table Material Label].[Total Weight]

FROM [Table Material Label]

WHERE  (([Table Material Label].[Date Recieved])>=[Forms]![Report Generator]![Text6] 
    And ([Table Material Label].[Date Recieved])<=[Forms]![Report Generator]![Text7]) 
    AND ([Table Material Label].Supplier = [Forms]![Report Generator]![Supp] 
    OR [Forms]![Report Generator]![Supp] IS NULL)

ORDER BY [Table Material Label].[Date Recieved], [Table Material Label].MaterialDescription, [Table Material Label].MaterialCode, [Table Material Label].Supplier;

Answer 1

看这里：https://stackoverflow.com/a/38899574/3820271

AND ([Table Material Label].Supplier = [Forms]![Report Generator]![Supp] 
     OR [Forms]![Report Generator]![Supp] IS NULL)

如果供应商标准为空，则此 AND 部分将始终为真。