我有一个参数，可以是3个可能值0、2或null中的1个（这些是枚举的值0处于挂起状态，1处于审核中，2处于关闭状态）。如果为空，则应检索所有状态，但如果为2，则应检索所有已关闭的状态；如果为0，则应检索挂起或正在审阅的状态。最后一个意味着我要检索状态为0或1的记录。我有以下代码到目前为止，并尝试与案件开关，但它不工作。

SELECT * FROM PurchaseOrder
    WHERE (CreationDate >= @StartDate AND CreationDate <= @EndDate)
    AND (@POStatus IS NULL OR [Status] = @POStatus)
    AND (@POStatus IS NULL OR [Status] = CASE @POStatus WHEN 0 THEN 1 END)
    AND (@PurchaseOrderIdSearch IS NULL OR PurchaseOrderId LIKE @PurchaseOrderIdSearch)
    AND EmployeeId = @EmployeeId
    ORDER BY CreationDate DESC, PurchaseOrderId DESC

我通过添加if语句解决了这个问题，我在寻找一种更简单的方法来避免重复，现在是这样的：

IF @POStatus = 0
    BEGIN
        SELECT * FROM PurchaseOrder
        WHERE (CreationDate >= @StartDate AND CreationDate <= @EndDate)
        AND (([Status] = @POStatus)
        OR ([Status] = 1))
        AND (@PurchaseOrderIdSearch IS NULL OR PurchaseOrderId LIKE @PurchaseOrderIdSearch)
        AND EmployeeId = @EmployeeId
        ORDER BY CreationDate DESC, PurchaseOrderId DESC
    END
    ELSE
    BEGIN
        SELECT * FROM PurchaseOrder
        WHERE (CreationDate >= @StartDate AND CreationDate <= @EndDate)
        AND (@POStatus IS NULL OR [Status] = @POStatus)
        AND (@PurchaseOrderIdSearch IS NULL OR PurchaseOrderId LIKE @PurchaseOrderIdSearch)
        AND EmployeeId = @EmployeeId
        ORDER BY CreationDate DESC, PurchaseOrderId DESC
    END