Null值處理

Question

假設我有一個查詢

SELECT val FROM tbl 

我想寫查詢，將輸出「ValueIsNotNull」當val爲NOT NULL和「ValueIsNull」當val爲null。是否可以用一行來完成。截至目前，我只找到ISNULL(val,'ValueIsNull') AS val1。但是，如果值不爲null，則會打印原始值。

Answer 1

select 
    case 
     when val is null then 'ValueIsNull' 
     else 'ValueIsNotNull' 
    end 
    as NewVal 
from tbl 

Answer 2

你想要的case語句功能：

select (case when val is NULL then 'ValueIsNull' else 'ValueIsNotNull' end) 

Answer 3

SELECT CASE WHEN val IS NULL THEN 'ValueIsNotNull' ELSE 'ValueIsNull' END