案例需求：

完成数据库插入，删除，修改，查看操作。

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分为 插入，删除，修改，查看，查询 几个模块。

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代码：

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QDebug>
#include <QSqlError>
#include <QDateTime>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget();
    void display();

private slots:
    void on_insert_button_clicked();

    void on_delete_button_clicked();

    void on_update_button_clicked();

    void on_query_button_clicked();

private:
    Ui::Widget *ui;
    QSqlDatabase db;
    QSqlQuery *query;
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    this->setWindowTitle("数据库可视化窗口");

    // 加载数据库的驱动
    db = QSqlDatabase::addDatabase("QSQLITE");
    // 设置本地数据库文件
    db.setDatabaseName("stu.db");
    // 打开数据库
    if(db.open())   qDebug()<<"打开成功....";
    else    qDebug()<<"打开失败....";
    // 向数据库发送sql语句
    query = new QSqlQuery; // 不可指定父对象
    if(query->exec("CREATE TABLE IF NOT EXISTS stu_info (id INT PRIMARY KEY,name STRING(32),score DOUBLE)"))
        qDebug()<<"创建table成功....";
    else    qDebug()<<"创建table失败:"<<query->lastError().text();
    // 显示
    display();
}

Widget::~Widget()
{
    delete ui;
    delete  query; // 因为调用时不能指定父对象，所以需要手动释放
    // 关闭数据库
    db.close();

}
// displlay
void Widget::display(){
    query->exec(QString("SELECT * FROM stu_info"));
    while(query->next()){
        int id = query->value("id").toInt();
        QString name = query->value("name").toString();
        double score = query->value("score").toDouble();
        ui->plainTextEdit->appendPlainText(QString("id : %1 | name : %2 | score : %3").arg(id).arg(name).arg(score));
    }
}
// insert
void Widget::on_insert_button_clicked(){
    QDateTime currentDate = QDateTime::currentDateTime();
    QString dateTimeString = currentDate.toString("yyyy-MM-dd hh:mm:ss");

    if(ui->num_edit->text() == "" || ui->name_edit->text() == "" || ui->score_edit->text() == ""){
        qDebug()<<"信息缺失 插入失败："<<query->lastError().text();
        ui->plainTextEdit->appendPlainText(QString("%1 信息缺失 插入失败....").arg(dateTimeString));
        return ;
    }
    int num = ui->num_edit->text().toInt();
    QString name = ui->name_edit->text();
    double score = ui->score_edit->text().toDouble();

    if(query->exec(QString("INSERT INTO stu_info VALUES('%1','%2','%3')").arg(num).arg(name).arg(score))){
        qDebug()<<dateTimeString<<"插入成功....";
        ui->plainTextEdit->appendPlainText(QString("%1 插入成功....").arg(dateTimeString));
        display();
    }
    else{
        qDebug()<<"插入失败："<<query->lastError().text();
        ui->plainTextEdit->appendPlainText(QString("%1 插入失败....").arg(dateTimeString));
    }
}
// delete
void Widget::on_delete_button_clicked()
{
    QDateTime currentDate = QDateTime::currentDateTime();
    QString dateTimeString = currentDate.toString("yyyy-MM-dd hh:mm:ss");
    if(ui->num_edit->text() == ""){
        qDebug()<<dateTimeString<<"学号不存在 删除失败....";
        ui->plainTextEdit->appendPlainText(QString("%1 学号不存在 删除失败....").arg(dateTimeString));
    }
    else if(query->exec(QString("DELETE FROM stu_info WHERE id = %1").arg(ui->num_edit->text().toInt()))){
        qDebug()<<dateTimeString<<"删除成功....";
        ui->plainTextEdit->appendPlainText(QString("%1 删除成功....").arg(dateTimeString));
        display();
    }
    else{
        qDebug()<<"删除失败："<<query->lastError().text();
        ui->plainTextEdit->appendPlainText(QString("%1 删除失败....").arg(dateTimeString));
    }
}
// update
void Widget::on_update_button_clicked()
{
    QDateTime currentDate = QDateTime::currentDateTime();
    QString dateTimeString = currentDate.toString("yyyy-MM-dd hh:mm:ss");

    if(query->exec(QString("UPDATE stu_info SET id = %1, name = '%2', score = %3 WHERE id = %4").arg(ui->num_edit->text().toInt()).arg(ui->name_edit->text()).arg(ui->score_edit->text().toDouble()).arg(ui->num_edit->text().toInt()))){
        qDebug()<<dateTimeString<<"更新成功....";
        ui->plainTextEdit->appendPlainText(QString("%1 更新成功....").arg(dateTimeString));
        display();
    }
    else{
        qDebug()<<"更新失败："<<query->lastError().text();
        ui->plainTextEdit->appendPlainText(QString("%1 更新失败....").arg(dateTimeString));
    }
}
// query
void Widget::on_query_button_clicked()
{//SELECT * FROM stu_info WHERE id = %1
    QDateTime currentDate = QDateTime::currentDateTime();
    QString dateTimeString = currentDate.toString("yyyy-MM-dd hh:mm:ss");

    if(query->exec(QString("SELECT * FROM stu_info WHERE id = %1").arg(ui->num_edit->text().toInt()))){
        qDebug()<<dateTimeString<<"查询成功....";
        ui->plainTextEdit->appendPlainText(QString("%1 查询成功....").arg(dateTimeString));
        // 显示
        while(query->next()){
        int id = query->value("id").toInt();
        QString name = query->value("name").toString();
        double score = query->value("score").toDouble();
        ui->plainTextEdit->appendPlainText(QString("id : %1 | name : %2 | score : %3").arg(id).arg(name).arg(score));
        }
    }
    else{
        qDebug()<<"查询失败："<<query->lastError().text();
        ui->plainTextEdit->appendPlainText(QString("%1 查询失败....").arg(dateTimeString));
    }
}

widget.ui

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输出：

初始界面：

插入：

修改：

删除：

查询：