Question

 Declare @CategoryID as int
BEGIN  
    SELECT 
    (CASE 
        WHEN EXISTS(
            SELECT t0.Categoryid AS [EMPTY]
            FROM Categories AS [t0]
            WHERE [t0].Categoryname = @CategoryName
           ) THEN 1
        ELSE 0
     END) AS [value]

如果我想用t0.Categoryid在变量内设置我的变量怎么能这样做呢？

我想要的是将然后1 替换为类别ID值...

提前感谢..

Answer 1

Declare @CategoryID as int
SET @CategoryID =  CASE WHEN EXISTS(SELECT 1
                                    FROM  Categories
                                    WHERE Categoryname = @CategoryName)
                     THEN 1 ELSE 0
                   END

另一种方式就是......

IF EXISTS (SELECT 1
           FROM  Categories
           WHERE Categoryname = @CategoryName)
 BEGIN
   SET @CategoryID = 1;
 END
ELSE
 BEGIN
   SET @CategoryID = 0;
 END

Answer 2

这将返回类别ID（如果存在），如果不存在则返回0。

SET @CategoryID = null;

SELECT @CategoryID = t0.Categoryid
FROM Categories AS [t0]
WHERE [t0].Categoryname = @CategoryName;

IF @CategoryID IS NULL
    SET @CategoryID = 0;

SELECT @CategoryID AS [value];

但是，如果不存在，我建议只返回null，或者返回一个额外的@Exists（BIT）来指示它是否存在。

Answer 3

我的2美分......

DECLARE @any BIT = 0
SELECT TOP 1 @any = 1 FROM Categories WHERE CategoryName = @CategoryName

IF (@any = 1)
  PRINT 'Yes'
ELSE
  PRINT 'No'

Answer 4

哟可以这样试试。

Declare @CategoryID as int
 Set @CategoryID =0;
    SELECT @CategoryID=t0.Categoryid
    FROM Categories AS [t0]
    WHERE [t0].Categoryname = @CategoryName

IF类别名称存在而不是指定该类别的类别ID，否则保持为零。

Answer 5

Declare @CategoryID as int
SET @CategoryID =
            (SELECT t0.Categoryid AS [EMPTY]
            FROM Categories AS [t0]
            WHERE [t0].Categoryname = @CategoryName)
SET @CategoryID =COALESCE(@CategoryID ,0)

Answer 6

您可以在几行中使用这种方法

DECLARE @CategoryID int
SELECT @CategoryID = Categoryid FROM Categories WHERE Categoryname = @CategoryName

IF @CategoryID IS NULL
    THROW 50000, N'not found', 1 -- do something
    
SELECT @CategoryID -- the Categoryid value

在存在条件sql server中设置变量值

6 个答案: