TSQLを使用して、DISTINCTレコードを並べ替えてから、行番号を適用します

これがあなたが探しているものだと思います：最大ActivationDateではない行番号を持つすべての行が必要です

DECLARE @tbl TABLE
(
    CustomerName    VARCHAR(20),
    ProductName     VARCHAR(20),
    KeyCode         INT,
    ActivationDate  DATETIME
)


INSERT INTO @tbl
SELECT 'cmp1', 'game', 28734, GETDATE() -1    UNION ALL
SELECT 'cmp1', 'game', 28734, GETDATE() -1.5  UNION ALL
SELECT 'cmp1', 'game', 28734, GETDATE() -1.2  UNION ALL
SELECT 'cmp1', 'game', 28734, GETDATE() -1.8  UNION ALL
SELECT 'cmp1', 'game', 28734, GETDATE()       UNION ALL
SELECT 'cmp1', 'game', 28734, GETDATE() -17   UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE() -1    UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE() -1.5  UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE() -1.2  UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE() -1.8  UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE()       UNION ALL
SELECT 'cmp2', 'game', 28736, GETDATE() -17     


SELECT        ROW_NUMBER() OVER(ORDER BY ActivationDate DESC) RowNumber,
              CustomerName, 
              ProductName, 
              KeyCode, 
              ActivationDate        
FROM @tbl workTable
WHERE ActivationDate != 
    (
        SELECT MAX(ActivationDate)
        FROM @tbl checkTable
        WHERE workTable.CustomerName = checkTable.CustomerName
            AND workTable.ProductName = checkTable.ProductName
            AND workTable.KeyCode = checkTable.KeyCode
    )

RowNumber     CustomerName     ProductName     KeyCode  ActivationDate
1             cmp1             game            28734    2011-02-24 08:40:45.790
2             cmp2             game            28736    2011-02-24 08:40:45.790
3             cmp2             game            28736    2011-02-24 03:52:45.793
4             cmp1             game            28734    2011-02-24 03:52:45.793
5             cmp1             game            28734    2011-02-23 20:40:45.790
6             cmp2             game            28736    2011-02-23 20:40:45.790
7             cmp2             game            28736    2011-02-23 13:28:45.790
8             cmp1             game            28734    2011-02-23 13:28:45.790
9             cmp1             game            28734    2011-02-08 08:40:45.790
10            cmp2             game            28736    2011-02-08 08:40:45.790

複数必要な場合...

SELECT  ROW_NUMBER() OVER(ORDER BY ActivationDate DESC) RowNumber,
        CustomerName, 
        ProductName, 
        KeyCode, 
        ActivationDate      
FROM @tbl workTable
WHERE NOT ActivationDate IN 
    (
        SELECT TOP 2 ActivationDate
        FROM @tbl checkTable
        WHERE workTable.CustomerName = checkTable.CustomerName
            AND workTable.ProductName = checkTable.ProductName
            AND workTable.KeyCode = checkTable.KeyCode
        ORDER BY ActivationDate DESC
    )