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（1）在student数据库上创建一个用户表tb_account，该表包含用户id，用户名和密码。
| 字段名称 | 数据类型 | 注释 | 约束 |
| user_id | Char(8) | 用户id | 主键 |
| user_name | char(10) | 用户名 | 不能为空 |
| password | char(10) | 密码 | 默认值：123456 |
（2） 将学生表tb_student表中的学号和姓名全部添加到用户表tb_account中。
参考完整代码如下：
import java.sql.*;public class case2 {static final String JDBC_DRIVER = "com.mysql.cj.jdbc.Driver";static final String DB_URL = "jdbc:mysql://localhost:3306/student";static final String USER = "user"; // 替换为你的用户名static final String PASS = "password"; // 替换为你的密码public static void main(String[] args) {Connection conn = null;try {// 加载 JDBC 驱动Class.forName(JDBC_DRIVER);// 建立连接conn = DriverManager.getConnection(DB_URL, USER, PASS);// 创建 tb_account 表String createTableSQL = "CREATE TABLE IF NOT EXISTS `tb_account` ("+ " `user_id` CHAR(8) NOT NULL,"+ " `user_name` CHAR(10) NOT NULL,"+ " `password` CHAR(10) NOT NULL DEFAULT '123456',"+ " PRIMARY KEY (`user_id`)"+ ")";try (Statement statement = conn.createStatement()) {statement.executeUpdate(createTableSQL);System.out.println("Table 'tb_account' created successfully.");}// 插入数据到 tb_account 表String insertSQL = "INSERT INTO `tb_account` (`user_id`, `user_name`)"+ " SELECT `stu_id`, `stu_name` FROM `tb_student`";try (Statement statement = conn.createStatement()) {int rowsAffected = statement.executeUpdate(insertSQL);if (rowsAffected > 0) {System.out.println("Data inserted successfully into 'tb_account'.");}}} catch (SQLException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();} finally {// 关闭数据库连接if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}}
}