code.txt

       QTimer *timer31= new QTimer(this);       //by  douya
             connect(timer31, SIGNAL(timeout()),this,SLOT(restoreDB()));
             timer31->start(60*1000);
             
             void Widget::restoreDB(){



    QSqlDatabase data_base = QSqlDatabase::addDatabase("QSQLITE");
    data_base.setlDatabaseName("qdg.db");
            if(!data_base.open())
                qDebug()<<"douya: failed to connect to ";
            else
            {
                qDebug()<<"douya:success";
            }
     QSqlQuery query(data_base);
     query.exec(QString("delete from   sys_log where logid not in  (select logid  from sys_log order by time desc limit 8000 );"));
     qDebug()<<"douya:ok";


}