为什么所有这些QSqlQuery属性都返回false？

我已经设置了这样的数据库，并确认正在从名为“person”的表中添加和读取记录：

db = QSqlDatabase::addDatabase("QSQLITE");
    db.setHostName("localhost");
    db.setDatabaseName("testDatabase.db");
    if (db.open()){

        checkTableExists("person"); //see below

        QSqlQuery query;
        query.exec("create table person (id int primary key, "
                       "firstname varchar(20), lastname varchar(20))");
        query.exec("insert into person values(101, 'Danny', 'Young')");
        query.exec("insert into person values(107, 'Christine', 'Holand2')");
        query.exec("insert into person values(103, 'Lars', 'Gordon')");
        query.exec("insert into person values(104, 'Roberto', 'Robitaille')");
        query.exec("insert into person values(105, 'Maria', 'Papadopoulos')");

        checkTableExists("person"); //see below

        QSqlQuery query2("SELECT lastname FROM person");
             while (query2.next()) {
                 QString lastname = query2.value(0).toString();
                 qDebug()<<lastname;
             }

    }else{ //handle problem }

现在要了解有关QSqlQuery的各种属性的更多信息，我制作了这个函数，我现在只用于调试：

bool checkTableExists(QString tablename)const{
    QString sqlQuery = QString("SELECT name FROM testDatabase.db WHERE type =:table AND name = :tablename ");
    QSqlQuery query;
    bool prepare=query.prepare(sqlQuery);
    query.bindValue(":table", "table");
    query.bindValue(":tablename", tablename);
    bool isExec=query.exec();

    qDebug()<<"prepare: "<<prepare;
    qDebug()<<"exec: " << isExec;
    qDebug()<<"first: " << query.first();
    qDebug()<<"isSelect: " << query.isSelect();
    qDebug()<<"isValid: " << query.isValid();
    qDebug()<<"isActive: " << query.isActive();
    qDebug() << "next:" << query.next();
    qDebug()<< "nextResult: "<<query.nextResult();
    qDebug()<<"numRowsAffectd: "<<query.numRowsAffected();

    return query.next();

}

当我运行上述内容时，我得到：

prepare:  false 
exec:  false 
first:  false 
isSelect:  false 
isValid:  false 
isActive:  false 
next: false 
nextResult:  false 
numRowsAffectd:  -1 
prepare:  false 
exec:  false 
first:  false 
isSelect:  false 
isValid:  false 
isActive:  false 
next: false 
nextResult:  false 
numRowsAffectd:  -1 
"Young" 
"Holand" 
"Gordon" 
"Robitaille" 
"Papadopoulos" 
"Holand2"

在创建表之前和之后，这些属性都不会返回true，为什么会这样？