java开发数据库 mysql

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MySQLConnectionTest {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "username";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            System.out.println("Connected to the database!");
        } catch (SQLException e) {
            System.out.println("Connection failed: " + e.getMessage());
        }
    }
}

-- 添加索引示例
CREATE INDEX idx_username ON users(username);

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class TransactionExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "username";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            conn.setAutoCommit(false);

            String sql1 = "UPDATE accounts SET balance = balance - 100 WHERE id = 1";
            String sql2 = "UPDATE accounts SET balance = balance + 100 WHERE id = 2";

            try (PreparedStatement ps1 = conn.prepareStatement(sql1);
                 PreparedStatement ps2 = conn.prepareStatement(sql2)) {

                ps1.executeUpdate();
                ps2.executeUpdate();

                conn.commit();
                System.out.println("Transaction committed successfully.");
            } catch (SQLException e) {
                conn.rollback();
                System.out.println("Transaction rolled back: " + e.getMessage());
            }
        } catch (SQLException e) {
            System.out.println("Connection failed: " + e.getMessage());
        }
    }
}