Add queries to retrieve person, credit and dette
Check if the person is alreay in the database before adding it
Check if the person is already present before starting to populate the database
Add a command to fetch the debt or credit of one personne
Add a query to fetch all the money associated to people
Add credit or debt only if it's not already present in the database
Refact: people -> person
Check if person exists before adding credit or debt in order to associate it to the right person id
Add methods to retrieve money data from the database
Temporarily use int for date in database
Add an interface between code and databse method