The database is lightweight and easy to use. The code is as follows:

#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QDebug>

static bool createConnection()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("my.db");
    if (!db.open()) {
        QMessageBox::critical(0, "Cannot open database1",
                              "Unable to establish a database connection.", QMessageBox::Cancel);
        return false;
    }
    QSqlQuery query;
    // Create a login user table
    query.exec("create table user (username varchar primary key, passwd varchar)");
    query.exec("insert into user values('admin', 'root')");
}

After compilation, a my.db database file is generated in the directory. There is a table named user in the database.

If two different database files are to be operated on at the same time, then:

#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlQuery>

static bool createConnection()
{
    // Create a database connection using "Connection 1" as the connection name
    QSqlDatabase db1 = QSqlDatabase::addDatabase("QSQLITE", "connection1");
    db1.setDatabaseName("my1.db");
    if (!db1.open()) {
        QMessageBox::critical(0, "Cannot open database1",
                              "Unable to establish a database connection.", QMessageBox::Cancel);
        return false;
    }

    // Here you specify the connection
    QSqlQuery query1(db1);
    query1.exec("create table student (id int primary key, "
                "name varchar(20))");
    query1.exec("insert into student values(0, 'LiMing')");
    query1.exec("insert into student values(1, 'LiuTao')");
    query1.exec("insert into student values(2, 'WangHong')");

    // To create another database connection, use a different connection name, here is "Connection 2"
    QSqlDatabase db2 = QSqlDatabase::addDatabase("QSQLITE", "connection2");
    db2.setDatabaseName("my2.db");
    if (!db2.open()) {
        QMessageBox::critical(0, "Cannot open database1",
                              "Unable to establish a database connection.", QMessageBox::Cancel);
        return false;
    }

    // Here you specify the connection
    QSqlQuery query2(db2);
    query2.exec("create table student (id int primary key, "
                "name varchar(20))");
    query2.exec("insert into student values(10, 'LiQiang')");
    query2.exec("insert into student values(11, 'MaLiang')");
    query2.exec("insert into student values(12, 'ZhangBin')");
    return true;
}

Connect to the SQL Server database:

Prerequisites:

Installed SQL Server 2008 and created database MyDB in SQL Server

Overview of Qt Connecting SQL Server 2008 through ODBC:

When Qt connects to database through ODBC, the database name used is not written directly to the database name, but DSN name.

There are two ways to use DSN names:

1. Configure DSN in operating system;

2. Using DSN connection string to connect ODBC database directly in Qt program code.

Here is a detailed description of how to connect SQL Server 2008 with DSN configuration in the operating system

Configuring DSN in Operating System

Which SQL Server server is the last one to connect to? If it has been configured in SQL Server 2008, the server will be selected.

The login ID and password here are the same as those configured in SQL Server 2008.

If a database has been established, there will be a database to be selected.

So far, the QTDSN has been configured.

The following configuration is then performed in the QT:

    QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
    QString dsn = QString::fromLocal8Bit("QTDSN");
    db.setHostName("127.0.0.1");
    db.setDatabaseName(dsn);
    db.setUserName("sa");
    db.setPassword("123456");

So far, the link is complete.

#include <QMessageBox>
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QDebug>

static bool createConnection()
{
    
    QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
    QString dsn = QString::fromLocal8Bit("QTDSN");
    db.setHostName("127.0.0.1");
    db.setDatabaseName(dsn);
    db.setUserName("sa");
    db.setPassword("123456");
    if (!db.open()) {
        QMessageBox::critical(0, "Cannot open database1",
                              "Unable to establish a database connection.", QMessageBox::Cancel);
        return false;
    }
    QSqlQuery query;
    // Create a login user table
    query.exec("select * from  user");
    while(query.next()){
	qDebug()<<query.value(0).toString();
	qDebug()<<query.value(1).toString();
    }
}