Question

我有一个包含列的表，它有四个记录：

Create Table dbo.Test(Name varchar(100));
Insert into dbo.Test Values ('A'),('B'),('C'),('D');

然后，问题是没有使用Row_Number窗口函数的行号，所以我使用：

Select Name,(Select Count(*) Over (Order By Name,NewID() Rows Between Unbounded Preceding and Current Row) as RowNumber
From dbo.Test

当然，它给了我正确的答案，但任何人都可以解释一下，为什么这可以有行号。因为我不在这里使用Partition By，所以dbo.Test表应该是一个数据集，每个记录的RowNumber应该是相同的4.请纠正我并解释一下。

Answer 1

你的答案在你自己的问题_ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW_中，这基本上意味着对于每一行，数据集都是当前行，所以计数应该是 rownumber 。

如果未设置窗口框架之前，则SQL会使用该窗口框架，如下面的示例代码所示：

declare  @Test Table(Name varchar(100));
Insert into @Test Values ('A'),('B'),('C'),('D'),('1');

SELECT Name
 , (COUNT(*) OVER (ORDER BY Name)) as RowNumberCorrect
, (COUNT(*) OVER (ORDER BY Name ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)) as RowNumberCorrect2
, (COUNT(*) OVER (ORDER BY Name ROWS BETWEEN UNBOUNDED PRECEDING AND 1 FOLLOWING)) as RowNumberWrong
, (COUNT(*) OVER (ORDER BY Name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)) as RowsCount
, (COUNT(*) OVER ()) as RowsCount2
FROM @Test

为什么Count（*）Over（Order by <column name =“”>）可以给出一个运行的toal？

1 个答案: