Sequential MySQL dumps and overwriting updated data

I'm looking to do MySQL dumps on a nightly basis. I already have a solution for outputting just a diff of the data, but what I need is a way to import the data back into MySQL so the data in MySQL is UPDATED, instead of INSERTED if it's already there. For example, here's a sample table:

Id | User | Account_Value | Created_At | Updated_At
1  | Bob  | $100          | 2009-01-01 | 2009-01-01
2  | Ed   | $200          | 2009-01-01 | 2009-01-01

Then the next day, the table looks like this:

Id | User | Account_Value | Created_At | Updated_At
1  | Bob  | $50           | 2009-01-01 | 2009-01-02
2  | Ed   | $200          | 2009-01-01 | 2009-01-01

When I do the data export on the second day, it will correctly output something like:

INSERT into ACCOUNTS VALUES (1,'Bob', '$50', '2009-01-01', '2009-01-02')

However, this will conflict with what's already there. What I want is to have it overwrite what's already there. Thoughts?