SQL View - 如果为空，则添加默认值？

Question

我正在生成一个 View ，如果单元格为空，我想用预定义值填充单元格。

View 的选择是:

SELECT a_case.Id, 
    R1.Type AS Referred_by_1,
    R1.Type AS Referred_by_2,
    R1.Type AS Referred_by_3
FROM dbo.CaseInfo a_case LEFT JOIN
    dbo.Referrer R1 ON P.Id = R1.Case_Id AND R1.Seq = 1 LEFT JOIN
    dbo.Referrer R2 ON P.Id = R2.Case_Id AND R2.Seq = 2 LEFT JOIN
    dbo.Referrer R3 ON P.Id = R3.Case_Id AND R3.Seq = 3 

引荐来源网址是可选的，如果未指定，我需要用“ND”填充该字段。

我想我也许应该使用 CASE WHEN，但我不确定如何将其集成到现有的选择中...

非常感谢您的任何建议! - L

Answer 1

您可以使用ISNULL :

SELECT a_case.Id,      
    ISNULL(R1.Type, 'ND') AS Referred_by_1,     
    ISNULL(R2.Type, 'ND') AS Referred_by_2,     
    ISNULL(R3.Type, 'ND') AS Referred_by_3 
FROM ...