Since you talked about QML I will assume that you work with embedded devices so SQLite is probably the database for you.
Here is an example of how to connect to a database, hope this helps:

QSqlDatabase db = QSqlDatabase::addDatabase("SQLITE"); db.setDatabaseName("path/to/database.db"); db.open(); //This will create the database if it doesent exist

Make sure to include

#include <QSqlDatabase>

Also add

QT += sql

To your project file