我有3列（分类，汇总，案例级建议）。目标是基于某些参数使用iif语句计算示例级别。我有基于参数的代码。但是，我想将当前参数应用于具有术语托盘的类别，并将另一个具有不同参数的代码集应用于具有术语设备的类别（托盘和设备在同一列中）。如何让代码只查看类别列中的信盒应用iif并添加另一个类似的iff以只查看类别列中的设备。
当前代码为：

SELECT [Calculated Total].casemain_id, [Calculated Total].category, 
Sum([Calculated Total].Total) AS SumOfTotal, IIf([SumOfTotal] <=3,
"A",IIf([SumOfTotal]>=9,"D",IIf([SumOfTotal]>=6,"C",IIf([SumOfTotal]       
>=4,"B","C")))) AS [Case Level Suggested]
FROM [Calculated Total]
GROUP BY [Calculated Total].casemain_id, [Calculated Total].category
ORDER BY [Calculated Total].casemain_id;

我一直在尝试添加where[calculated total].category='instrument trays'；但总是会出错。