This will query for a specific CheckingAccount, and will return the number of the last associated account related CheckingAccount number.
Unless the same account owner is trying to open an account in 2 diferent places, there should be no problem, i guess...
For instance: An CheckingAccount number 2. When the owner wants to create a SavingAccount related to that account number 2, before inserting the entry in the database,
the method will query to see the max value of all the accounst associated with 2, and return the value.
If and CheckingAccountNumerber = 3, wants to do the same in the same time, the method will query for the accountNumber = 3, them return the value related to the accountNumber 3.