QSQLITE database can't exec queries

[mcwar]

Why this code is not working?

db = QSqlDatabase::addDatabase("QSQLITE"); //I defined the "db" at header.
    db.setDatabaseName("../database");
    db.open();
    QSqlQuery query(db);
    query.exec("SELECT id FROM lesson");
    QMessageBox::about(0,"",query.value(0).toString());

db = QSqlDatabase::addDatabase("QSQLITE"); //I defined the "db" at header.
    db.setDatabaseName("../database");
    db.open();
    QSqlQuery query(db);
    query.exec("SELECT id FROM lesson");
    QMessageBox::about(0,"",query.value(0).toString());

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code is running without any error but value which in message box is null. There is no result at query value.