sql数据库服务器怎样连接

mysql -h hostname -u username -p password -P port -D database_name

import pymysql

connection = pymysql.connect(
    host='hostname',
    user='username',
    password='password',
    db='database_name',
    charset='utf8mb4',
    cursorclass=pymysql.cursors.DictCursor
)

try:
    with connection.cursor() as cursor:
        sql = "SELECT * FROM table_name"
        cursor.execute(sql)
        result = cursor.fetchall()
        print(result)
finally:
    connection.close()

import java.sql.*;

public class DatabaseConnector {
    public static void main(String[] args) {
        String url = "jdbc:mysql://hostname:port/database_name";
        String user = "username";
        String password = "password";

        try {
            Connection conn = DriverManager.getConnection(url, user, password);
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM table_name");
            while (rs.next()) {
                System.out.println(rs.getString("column_name"));
            }
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}