sql-server - 如何添加一个新列，根据 SQL Server 中另一列的值标记列的重复项？

Question

我正在尝试通过添加一个列来修改表，该列可以标记所有重复项 Runner_Name基于 Track_Num .我尝试使用:

SELECT [Track_Num],
       ROW_NUMBER() OVER (PARTITION BY [Track_Num] ORDER BY [Runner_Name]) - 1 As Dup,
       [Runner_Name]
  FROM [runner]

但它不起作用，它只是对 Runner_Name 进行排序

表runner看起来像这样:

Track_Num     Runner_Name
   1            John
   1            John
   1            Jack
   2            Amy
   2            Mary
   2            John
   3            Josh
   3            Josh
   3            Taylor

我希望得到的所需表是:

Track_Num     Runner_Name    Dup
   1            John          1
   1            John          1
   1            Jack          NULL
   2            Amy           NULL
   2            Mary          NULL
   2            John          NULL
   3            Josh          1
   3            Josh          1
   3            Taylor        NULL

Answer 1

也许只是将窗口函数包装在 sign(nullif( ... ,1)) 中

示例

Select *
      ,Dup = sign(NullIf(sum(1) over (partition by  [Track_Num],[Runner_Name] ) ,1))
 From [runner]

退货

Track_Num   Runner_Name Dup
1   Jack    NULL
1   John    1
1   John    1
2   Amy     NULL
2   John    NULL
2   Mary    NULL
3   Josh    1
3   Josh    1
3   Taylor  NULL