如何删除数据库中的冗余数据（翻译）

如何删除数据库中的冗余数据（翻译） (15)             FirstName ORDER BY RecDate DESC, ID) AS SeqNumber
         FROM
        (SELECT ID, LastName, FirstName, RecDate
            FROM Customers
            WHERE (LastName, FirstName) IN
            (SELECT LastName, FirstName
               FROM Customers
               GROUP BY LastName, FirstName
               HAVING COUNT(*) > 1)))
        WHERE SeqNumber > 1);

这种技术保证了你可以控制每一个表中的保留的组，假设你有一个数据库，有一个促销或者有一个折扣信息，比如一个团体可以使用这种促销５次，或者个人可以使用这个折扣三次，为了指出要保留的组的个数，你可以在where 和having子句中进行设置，那么你将删除所有大于你设置有数的冗余组
DELETE
  FROM Customers
  WHERE ID IN
  (SELECT ID
      FROM
      (SELECT ID, LastName, FirstName,
         RANK() OVER (PARTITION BY LastName,
            FirstName ORDER BY ID) AS SeqNumber
         FROM
        (SELECT ID, LastName, FirstName
            FROM Customers
            WHERE (LastName, FirstName) IN
            (SELECT LastName, FirstName
               FROM Customers
               GROUP BY LastName, FirstName