Question

我现在正在使用Microsoft SQL，我的代码是：

   SELECT TOP 1 
   [avail]
   FROM [table1]
   where [name] = 'abc'
   order by [datetime] desc

我希望当[avail]存在时，返回[avail]的值，如果不存在，则返回0或“Not Found”

谢谢！

Answer 1

您可以使用此

SELECT ISNULL(( SELECT TOP 1 
   [avail]
   FROM [table1]
   where [name] = 'abc'
   order by [datetime] desc), 0) AS [avail]

Answer 2

您可以通过两种方式完成：

使用IF EXISTS方式：

IF EXISTS (SELECT TOP 1 [avail] FROM [table1] WHERE [name] = 'abc' ORDER BY [datetime] DESC)
    SELECT TOP 1 [avail] FROM [table1] WHERE [name] = 'abc' ORDER BY [datetime] DESC
ELSE 
    SELECT 0 AS [avail]

或将avail值存储到变量和进程中，这样唯一的风险是，如果top 1 avail返回空值，那么您将得到的结果为零。

DECLARE @Avail AS VARCHAR(100) = ''; -- varchar of the `avail` data size

SELECT TOP 1 @Avail = [avail] FROM [table1] WHERE [name] = 'abc' ORDER BY [datetime] DESC;

IF @Avail = ''
    SELECT 0 AS [avail]
ELSE 
    SELECT @Avail AS [avail]

Answer 3

尝试使用COALESCE。它从第一个具有非空值的参数中选择数据。如果avail不为null，则返回[avale]，否则返回“Not Found”

SELECT COALESCE(avail, 'Not Found')
FROM table1
WHERE name = 'abc'
ORDER BY datetime desc

您可以在https://docs.microsoft.com/en-us/sql/t-sql/language-elements/coalesce-transact-sql

中阅读有关COALESCE的内容

Answer 4

如果你想要它的前1或删除顶部命令

 SELECT TOP 1 
   isnull([avail],'0')
   FROM [table1]
   where [name] = 'abc'
   order by [datetime] desc

如果没有找到记录，则SQL select返回0，否则返回值

4 个答案: