数据库设计的代码，连接的是金仓数据库

以下是一个简单的数据库设计代码，使用的是金仓数据库：

#include <QSqlDatabase>
#include <QSqlQuery>

// 连接数据库
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
db.setHostName("localhost");
db.setDatabaseName("your_database_name");
db.setUserName("your_username");
db.setPassword("your_password");

// 打开数据库
if (!db.open()) {
    qDebug() << "Failed to open database";
    return;
}

// 创建用户表
QSqlQuery query;
query.exec("CREATE TABLE users ("
           "id INT PRIMARY KEY AUTO_INCREMENT,"
           "username VARCHAR(50) NOT NULL,"
           "password VARCHAR(50) NOT NULL,"
           "email VARCHAR(50) NOT NULL)");

// 创建试题表
query.exec("CREATE TABLE questions ("
           "id INT PRIMARY KEY AUTO_INCREMENT,"
           "title VARCHAR(100) NOT NULL,"
           "option_a VARCHAR(50) NOT NULL,"
           "option_b VARCHAR(50) NOT NULL,"
           "option_c VARCHAR(50) NOT NULL,"
           "option_d VARCHAR(50) NOT NULL,"
           "answer VARCHAR(50) NOT NULL)");

// 创建考试表
query.exec("CREATE TABLE exams ("
           "id INT PRIMARY KEY AUTO_INCREMENT,"
           "title VARCHAR(100) NOT NULL,"
           "start_time DATETIME NOT NULL,"
           "end_time DATETIME NOT NULL)");

// 创建考试-试题关联表
query.exec("CREATE TABLE exam_questions ("
           "exam_id INT NOT NULL,"
           "question_id INT NOT NULL,"
           "PRIMARY KEY (exam_id, question_id),"
           "FOREIGN KEY (exam_id) REFERENCES exams(id),"
           "FOREIGN KEY (question_id) REFERENCES questions(id))");

这段代码使用了QSqlDatabase类和QSqlQuery类来连接和操作数据库。其中，创建了四个表格：users、questions、exams和exam_questions，分别用于存储用户信息、试题信息、考试信息和考试-试题关联信息。您可以根据具体需求进行修改和完善。同时，需要注意的是，由于金仓数据库与MySQL数据库在数据类型、SQL语法等方面存在一些差异，可能需要进行一些调整和修改。