数据库删除操作

//删除操作的槽
void Widget::on_delbt_clicked()
{
    QString sql;
    if(ui->idedit->text()==NULL)
    {
        sql = "drop Stu";
    }
    else
    {
        sql = QString("delete from Stu where id = %1").arg(ui->idedit->text());
    }
    QSqlQuery query;
    if(!query.exec(sql))
    {
        QMessageBox::information(this,"提示","删除失败");
    }else
    {
        QMessageBox::information(this,"提示","删除成功");
    }

}

数据库查找操作

void Widget::on_updatebt_clicked()
{
    QString sql;
    //获取ui界面信息
    int ui_id = ui->idedit->text().toInt();
    QString ui_name = ui->nameedit->text();
    QString ui_sex = ui->sexedit->text();
    double ui_score = ui->scoreedit->text().toDouble();

    //判断要更新的数据
    if(ui_name!=NULL&&ui_sex!=NULL&&ui_score!=NULL)
    {
        sql = QString("update Stu set name = '%1',sex = '%2',score = %3 where id = %4").
                arg(ui->nameedit->text()).arg(ui->sexedit->text()).arg(ui->scoreedit->text()).arg(ui->idedit->text());
    }
    else if(ui_name!=NULL)
    {
        if(ui_sex!=NULL)
        {
            sql = QString("update Stu set name = '%1',sex = '%2' where id = %3").
                    arg(ui->nameedit->text()).arg(ui->sexedit->text()).arg(ui->idedit->text());
        }
        else if(ui_score!=NULL)
        {
            sql = QString("update Stu set name = '%1',score = %2 where id = %3").
                    arg(ui->nameedit->text()).arg(ui->scoreedit->text()).arg(ui->idedit->text());
        }
        else if(ui_sex==NULL&&ui_score==NULL)
        {
            sql = QString("update Stu set name = '%1' where id = %2").
                    arg(ui->nameedit->text()).arg(ui->idedit->text());
        }
    }
    else if(ui_name==NULL)
    {
        if(ui_sex!=NULL&&ui_score!=NULL)
            sql = QString("update Stu set sex = '%1',score = %2 where id = %3").
                    arg(ui->sexedit->text()).arg(ui->scoreedit->text()).arg(ui->idedit->text());
        else if(ui_sex==NULL)
        {
            sql = QString("update Stu set score = '%1' where id = %2").
                    arg(ui->scoreedit->text()).arg(ui->idedit->text());
        }
        else if(ui_score==NULL)
        {
            sql = QString("update Stu set score = '%1',score = %2 where id = %3").
                    arg(ui->scoreedit->text()).arg(ui->idedit->text());
        }
    }
    else if(ui_id==NULL)
    {
        QMessageBox::information(this,"提示","请输入id");
    }
    //准备sql语句
    QSqlQuery query;
    if(!query.exec(sql))
    {
        QMessageBox::information(this,"提示","更新失败");
    }else
    {
        QMessageBox::information(this,"提示","更新成功");
    }
}