I have populated a combobox with an QSqlQueryModel. It's all working fine as it is, but I would like to add an extra item to the combobox that could say "ALL_RECORDS". This way I could use the combobox as a filtering device. 
I obviously don't want to add this extra item in the database, how can I add it to the combobox after it's been populated by a model?
You could use a proxy model that takes gets it's data from two models, one for your default values, the other for your database, and use it to populate your QComboBox.
Adding an item to an already populated combobox