Question

我有一张这样的表：

    CREATE TABLE [dbo].[Scores](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [Score] [float] NULL,
 CONSTRAINT [PK_Scores] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

我有一些INSERT

INSERT INTO Scores (Score) VALUES ( 0.5)
INSERT INTO Scores (Score) VALUES ( 2)
INSERT INTO Scores (Score) VALUES ( 3)
INSERT INTO Scores (Score) VALUES ( 4.5)

然后我意识到我需要改变所有得分，其中0.5应为2等。所以，我用光标来帮助我。像这样：

DECLARE @id int  
DECLARE @score float
DECLARE myCursor CURSOR LOCAL FAST_FORWARD FOR     

SELECT Id, Score      
FROM [dbo].[Scores]
OPEN myCursor FETCH NEXT FROM myCursor INTO @id, @score 
WHILE @@FETCH_STATUS = 0 
BEGIN     
    PRINT 'Id: ' PRINT @id    
    PRINT 'Score: ' PRINT @score       
    -- do your tasks here      
    FETCH NEXT FROM myCursor INTO @id, @score

    IF @score = 2 
    BEGIN 
        UPDATE Scores set Score = 3.0 WHERE Id = @id
    END
    IF @score = 3 
    BEGIN 
        UPDATE Scores set Score = 4.0 WHERE Id = @id
    END
    IF @score = 0.5
    BEGIN 
        UPDATE Scores set Score = 2.0 WHERE Id = @id
    END
    IF @score = 4.5
    BEGIN
        UPDATE Scores set Score = 5.0 WHERE Id = @id
    END
END  
CLOSE myCursor DEALLOCATE myCursor

在您提出更好的解决方案之前，请告诉我原因这行永远不会被调用：

UPDATE Scores set Score = 2.0 WHERE Id = @id

Answer 1

Update Scores
Set Score = 
  case 
    when Score = 0.5 then 2
    when Score = 4.5 then 5
    --etc...
    else Score
  end;

编辑：对不起，错过了它。

答案是因为提取错误。把

FETCH NEXT FROM myCursor INTO @id, @score

在光标循环的底部。您在循环外部获取第1行，在顶部再次获取第1行（但在打印出值后）。

Answer 2

舍入错误是可能的。如果您尝试将分数声明为十进制列（和变量）而不是浮点数，会发生什么？

T-sql：无法理解为什么IF子句永远不会被调用

2 个答案: