SQL视图 - 如果为null,则添加默认值？

Question

我正在生成一个视图,如果它们为null,我想用预定义的值填充单元格.

视图的选择是:

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 

引用者是可选的,如果没有指定,我需要用'ND'填充该字段.

我想我可能应该使用CASE WHEN,但我不确定如何将其整合到现有的选择中......

任何建议都感激不尽! - L.

Answer 1

你可以使用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 ...

Answer 2

使用COALESCE例如

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