For the following questions 7, 8, and 9, suppose a registration website creates data with the following fields for each person registered (note: if the user does not input a value, NULL is stored instead): Name, Date, Address, and Account Number. Suppose we collect data month by month. Each month, we would have a batch of data containing the fields listed above. At the end of the year, we want to summarize our registrant activities for the entire year, so we would remove redundancies in our data by removing any records with duplicate account numbers from month to month. What type of operation do we use in this scenario?