Question

在没有返回结果时返回字符串的正确方法是什么。以下不起作用

SELECT 
TOP 1 CASE
WHEN
    CustomerName IS NULL
        THEN 
            'Unknown'
WHEN
    CustomerName = ''
        THEN
            'Unknown'
ELSE 
    CustomerName
END
AS
CustomerName FROM CUSTOMER WHERE CustomerCode = 222

Answer 1

如果您的表格中没有Unknown的行不是CustomerName或NULL，那么您似乎想要返回''。

SELECT COALESCE((SELECT TOP 1 CustomerName FROM 
            CUSTOMER WHERE CustomerCode = 222
            AND CustomerName IS NOT NULL
            AND CustomerName <> ''),'Unknown') CustomerName

Answer 2

如果我理解了这个问题，即使WHERE子句不匹配，你想要返回一个值，并且你想要＆＃39; Unknown＆＃39;替换空字符串或NULL值：

SELECT TOP 1 COALESCE(NULLIF(CustomerName,''),'Unknown')
FROM (
  SELECT CustomerName FROM CUSTOMER WHERE CustomerCode = 222
  UNION ALL
  SELECT NULL
) t
ORDER BY CustomerName DESC

Answer 3

试试这可能是它的工作..

    SELECT DISTINCT TOP 1 CASE WHEN ISNULL(CustomerName,'') <>'' THEN CustomerName ELSE 'Unknown'
 END as CustomerName FROM CUSTOMER WHERE CustomerCode = 222

或

SELECT TOP 1 CustomerName FROM 
(SELECT DISTINCT TOP 1 CASE WHEN ISNULL(CustomerName,'') <>'' THEN CustomerName ELSE 'Unknown'
 END as CustomerName ,1 No FROM CUSTOMER WHERE CustomerCode = 222
UNION 
SELECT 'Unknown',2)
AS T ORDER BY No

没有结果时返回字符串

3 个答案: