void AddDialog::itemChanged(QTableWidgetItem current,QTableWidgetItem previous){
if(previous != NULL){
int index = previous->row();
int column =previous->column();
QSqlQuery query(db);
QString sqlStr = "select * from ";
QString table = ui->TableCombo->itemText(ui->TableCombo->currentIndex());
sqlStr += table;
QMessageBox box;
if(!query.exec(sqlStr)){

      box.setText(query.lastError().text());
      box.exec();
      return ;
 }


 query.seek(index);
 query.record().setValue(column,previous->text()); 
}

}
//这里的db是QDatabase类型的数据库对象 已经确认数据库正确连接,而且可以使用query.exec()执行更新的SQL语句没有问题.为什么setValue会没有效果