QSqlDatabase db=QSqlDatabase::addDatabase("QSQLITE","news");
db.setDatabaseName("tobacco.db");
QSqlQuery shownews(db);
shownews.exec("select * from Notifyinfo Order by InDate desc");
qDebug() <<"news' num is " <<shownews.numRowsAffected();//这句就总是显示news' num is 0