Showing Icon and tooltip into QSqlQueryModel index

Dear to all,
I need to insert an icon into every index of a QSqlQueryModel (so I can retrieve them from DB but mark them with the icon).
I need something like QStandardItem (const QIcon &icon, const QString &text) constructor, but I don't know how can I subclass It.
I need also to activate the tooltip on some columns.

I tried to see something of code of QSqlQueryModel and the structure of model classes but I'm a beginner and i lose myself on it :(

Why each model have more classes nested on it? There is a QSqlQueryModelPrivate, QSqlQueryModelItem ecc. How can use it? :(
Could you send a small example or more documentation of this?

Thanks for your time

Michele