Use QT to connect to MySQL and create table numbers, write data, and delete data

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Preface

MySQL Importance
Linux As an operating system ,Apache or Nginx As Web The server ,MySQL As a database ,PHP/Perl/Python As a server-side script interpreter . Because these four software are free or open source software （FLOSS), So it doesn't cost a cent （ Apart from the labor cost ） You can build a stability 、 Free website system , Known in the industry as “LAMP“ or “LNMP” Combine .

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One 、 Introduction to Qt And MySql The connection of

Basically ,Qt Same as X Window Upper Motif,Openwin,GTK Graphical interface library and Windows On the platform MFC,OWL,VCL,ATL It's the same kind of thing .
On this basis , We're doing it Ubuntu Embedded development , Better can choose MysQl The server .

Two 、 complete Qt And MySql The connection of services needs to meet

• install MySql And set up the environment
• install Qt And set the applicable and MySql Environment
• If Qt Report errors ：QMYSQL driver not loaded
  1、 The solution is to take MySql Of libmysql.dll Copy to the corresponding compiler
  

2、 Be careful ：QT Selected Windows32 Bits should correspond to 32 Bit libmysql.dll.

3、 Be careful ：QT Selected Windows64 Bits should correspond to 64 Bit libmysql.dll.

4、 Be careful ： It needs to be in the engineering documents xxxx.pro Add QT += sql As shown in the figure below
5、 Be careful ： choice C:\mysql-5.7.37-win32\lib Medium libmysql.dll copy to C:\Qt\Qt5.9.0\5.9\mingw53_32\bin in （ Remember that the corresponding is 32 A still 64 Bit Be sure to match ）libmysql.dll.

Qt Source code mainwindow.h

The code is as follows （ Example ）：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QMainWindow>
#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
#include <QDebug>
#include <QLineEdit>
#include <QPushButton>
#include <QLabel>
#include <QGridLayout>

namespace Ui {
    
class MainWindow;
}

class MainWindow : public QMainWindow
{
    
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

public:
   void myLayout();

private  slots:

   void button_1_clicked();
   void button_2_clicked();
   void button_3_clicked();
   void button_4_clicked();

protected:
    QLabel  *Label_1;
    QLabel  *Label_2;
    QLabel  *Label_3;
    QLabel  *Label_4;

    QLineEdit *Line_1;
    QLineEdit *Line_2;
    QLineEdit *Line_3;
    QLineEdit *Line_4;

    QPushButton *Button_1;
    QPushButton *Button_2;
    QPushButton *Button_3;
    QPushButton *Button_4;

};

#endif // MAINWINDOW_H

Qt Source code main.cpp

The code is as follows （ Example ）：

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    w.setFixedSize(300,200);
    w.setWindowTitle("MySql Connection tool ");
    w.myLayout();
    return a.exec();
}

Qt Source code mainwindow.cpp

The code is as follows （ Example ）：

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    
    delete ui;
}


void MainWindow::myLayout()
{
    
    QWidget *centerWindow = new QWidget;
    this->setCentralWidget(centerWindow);

    Button_1 = new QPushButton(" Connect MySql");
    Button_2 = new QPushButton(" Add data ");
    Button_3 = new QPushButton(" Update data ");
    Button_4 = new QPushButton(" Delete data ");


    Line_1 = new QLineEdit;
    Line_2 = new QLineEdit;
    Line_3 = new QLineEdit;
    Line_4 = new QLineEdit;

    Label_1 = new QLabel("id");
    Label_2 = new QLabel("name");
    Label_3 = new QLabel("age");
    Label_4 = new QLabel("score");

    Button_1->setMinimumHeight(50);
    Button_2->setMinimumHeight(50);
    Button_3->setMinimumHeight(50);
    Button_4->setMinimumHeight(50);


    connect(Button_1,SIGNAL(clicked(bool)),this,SLOT(button_1_clicked()));
    connect(Button_2,SIGNAL(clicked(bool)),this,SLOT(button_2_clicked()));
    connect(Button_3,SIGNAL(clicked(bool)),this,SLOT(button_3_clicked()));
    connect(Button_4,SIGNAL(clicked(bool)),this,SLOT(button_4_clicked()));

    QGridLayout *layout = new QGridLayout;

    layout->addWidget(Line_1,0,1,1,3,Qt::Alignment());
    layout->addWidget(Line_2,1,1,1,3,Qt::Alignment());
    layout->addWidget(Line_3,2,1,1,3,Qt::Alignment());
    layout->addWidget(Line_4,3,1,1,3,Qt::Alignment());

    layout->addWidget(Button_1,4,0,Qt::Alignment());
    layout->addWidget(Button_2,4,1,Qt::Alignment());
    layout->addWidget(Button_3,4,2,Qt::Alignment());
    layout->addWidget(Button_4,4,3,Qt::Alignment());


    layout->addWidget(Label_1,0,0,Qt::Alignment());
    layout->addWidget(Label_2,1,0,Qt::Alignment());
    layout->addWidget(Label_3,2,0,Qt::Alignment());
    layout->addWidget(Label_4,3,0,Qt::Alignment());


    layout->setMargin(12);
    centerWindow->setLayout(layout);
}

void MainWindow::button_1_clicked()
{
    
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName("127.0.0.1");// database server ip
    db.setUserName("root");// Database user name 
    db.setPassword("123456");// Database password 
    db.setDatabaseName("mydata");// Which database to use 
    // Use the default port number 3306 Well , Because locally 
    if( !db.open() )// Open database , If you return false Open failed 
    {
    
        QMessageBox::warning(this," error ",db.lastError().text() );// Open the failure , Display error message 
        return;
    }else
    {
    
        QMessageBox::warning(this," Congratulations ~~~","Mysql Successful connection ！");
    }

    QSqlQuery query;
    QString sql = "create table student(id int primary key auto_increment,name varchar(255),age int,score int);";
    query.exec(sql);

}

void MainWindow::button_2_clicked()
{
    
    int id = Line_1->text().toInt();
    QString name = Line_2->text();
    int age = Line_3->text().toInt();
    int score = Line_4->text().toInt();
    QString sql = QString("insert into student(id,name,age,score) values('%1','%2','%3','%4')").arg(id).arg(name).arg(age).arg(score);
    QSqlQuery query;
    query.exec(sql);

}

void MainWindow::button_3_clicked()
{
    

        int id = Line_1->text().toInt();
        QString name = Line_2->text();
        int age = Line_3->text().toInt();
        int score = Line_4->text().toInt();
        QString sql = QString("update student set id='%1',name='%2',age='%3',score='%4' where id='%5'").arg(id).arg(name).arg(age).arg(score).arg(id);
        QSqlQuery query;
        query.exec(sql);


}

void MainWindow::button_4_clicked()
{
    

        int id = Line_1->text().toInt();
        QString sql = QString("delete from student where id = '%1'").arg(id);
        QSqlQuery query;
        query.exec(sql);


}

Effect real picture

Operation method

• Copy the code into the project .
• Download the project package and import it directly .

Project package free download link

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The method of importing packages is shown in the following figure

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MySql Environment settings and verification tools are added 、 Delete data function .

MySql Environment setting and qt Tool validation diagram link