Question

在下面的示例中，列＆＃39; SecondColumn＆＃39;和＆＃39; ThirdColumn＆＃39;每次代码块运行时都会更新。＆＃39; FirstColumn＆＃39;将更新为存储在变量@NumberOfRows中的值（只要它> 0）。

我遇到的问题是当@NumberOfRows为0或更低时，＆＃39; FirstColumn＆＃39;将被设置为NULL。

是否有可能对此进行调整，以便@NumberOfRows为0或更小，那么＆＃39; FirstColumn＆＃39;根本不更新而不是将列设置为NULL？

DECLARE 
     @NumberOfRows INT = 0
    ,@NewValue DATETIME = GETDATE()
    ,@Other INT = 99

BEGIN
    UPDATE x
    SET  x.FirstColumn = (CASE WHEN @NumberOfRows > 0 THEN @NewValue END)
        ,x.SecondColumn = SYSDATETIMEOFFSET()
        ,x.ThirdColumn = @Other
    FROM TestTable x
    WHERE x.ID = 100
END

Answer 1

最简单的方法是使用当前值更新字段。

DECLARE 
     @NumberOfRows INT = 0
    ,@NewValue DATETIME = GETDATE()
    ,@Other INT = 99

BEGIN
    UPDATE x
    SET  x.FirstColumn = (CASE WHEN @NumberOfRows > 0 THEN @NewValue ELSE x.FirstColumn END)
        ,x.SecondColumn = SYSDATETIMEOFFSET()
        ,x.ThirdColumn = @Other
    FROM TestTable x
    WHERE x.ID = 100
END

Answer 2

如果@NumberOfRows <= 0：

，请勿执行给定列的更新

DECLARE 
     @NumberOfRows INT = 0
    ,@NewValue DATETIME = GETDATE()
    ,@Other INT = 99

BEGIN

    IF @NumberOfRows > 0
        BEGIN
            UPDATE x
            SET  x.FirstColumn = @NewValue
                ,x.SecondColumn = SYSDATETIMEOFFSET()
                ,x.ThirdColumn = @Other
            FROM TestTable x
            WHERE x.ID = 100
        END
    ELSE
        BEGIN
            UPDATE x
            SET  x.SecondColumn = SYSDATETIMEOFFSET()
                ,x.ThirdColumn = @Other
            FROM TestTable x
            WHERE x.ID = 100
        END
END

SQL Server 2012 - 如果满足条件，则更新列（CASE）否则不更新

2 个答案: