带 OR 的 SQL CASE 语句？

Question

说我必须遵循:

Select OrderID = 
    Case OrderID 
        When 1 Then 'Customer1'
        When 2 Then 'Customer2'
        When 3 Then 'Customer2'
        Else 'Unknown Customer'
    End 
From OrdersPlaced

是否可以添加一个 or 并执行以下操作:

Select OrderID = 
    Case OrderID 
        When 1 Then 'Customer1'
        When 2 Or 3 Then 'Customer2'
        Else 'Unknown Customer'
    End 
From OrdersPlaced

Answer 1

CASE 有两种形式表达式，“搜索”和“简单”。您不能使用 OR带有“简单”CASE表达式，但您可以使用“搜索”形式:

Case  
    When OrderID = 1 Then 'Customer1'
    When OrderID = 2 Or
         OrderID = 3 Then 'Customer2'
    Else 'Unknown Customer'
End 

甚至

Case  
    When OrderID = 1 Then 'Customer1'
    When OrderID IN (2, 3) Then 'Customer2'
    Else 'Unknown Customer'
End