case语句返回0而不是空字符串

Question

我有以下案例说明；

case when (
    CASE 
    WHEN datediff(year,view_3.[PERSON BIRTH DATE], @ReportPeriodStartDate)  >= 19 AND view_3.[NI NUMBER] IS NOT NULL 
        THEN '' ELSE view_3.[NI NUMBER]  END ) = 0 then '' else view_3.[NI NUMBER] END AS [NI NUMBER],

我希望它回来

Birthddate  NI Number   

14/04/2012  9000
06/05/2020  2000
01/01/2001
22/12/1998  

但是我得到的输出是;

Birthddate  NI Number   

14/04/2012  9000
06/05/2020  2000
01/01/2001  0
22/12/1998  0

我不想要零，我想要空字符串。

Answer 1

您想返回一个字符串，因此需要强制转换else：

else cast(view_3.[NI NUMBER] as varchar(255))