create table s_salary_shift (f_id integer primary key auto_increment, f_formula json);
insert into s_salary_shift(f_formula, '{"fixed":5000}'

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName("127.0.0.1");
    db.setDatabaseName("cafe5");
    db.setUserName("root");
    db.setPassword("******");
    if (!db.open()) {
        return;
    }
    QSqlQuery *q = new QSqlQuery(db);
    q->prepare("select f_formula from s_salary_shift where f_id=:f_id");
    q->bindValue(":f_id", 1);
    q->exec();
    if (q->next()) {
        qDebug() << q->value(0);
    } else {
        qDebug() << "Empty result";
    }