PHP怎么进行数据库的查询遍历

$mysql_host = 'localhost';//数据库所在的主机名
$mysql_user = 'root';//登录数据库的用户名
$mysql_password = '123456';//登录数据库的密码
$mysql_database = 'test';//数据库名

$con = mysqli_connect($mysql_host,$mysql_user,$mysql_password,$mysql_database);//连接数据库
if(mysqli_connect_errno($con)){//连接失败
    echo "连接数据库失败:".mysqli_connect_error();
}

$sql = "SELECT * FROM user";//查询user表中的所有数据
$result = mysqli_query($con,$sql);//执行查询语句

while($row = mysqli_fetch_array($result)){
    echo $row['id'].' '.$row['name'].' '.$row['age'].'<br>';//输出每一行数据
}

$sql = "SELECT * FROM user WHERE id=2";//查询id为2的用户数据
$result = mysqli_query($con,$sql);

$sql = "SELECT * FROM user ORDER BY age ASC";//按照年龄升序排序
$result = mysqli_query($con,$sql);

$sql = "SELECT * FROM user LIMIT 5";//查询前五条用户数据
$result = mysqli_query($con,$sql);

$sql = "SELECT AVG(age) FROM user";//查询用户平均年龄
$result = mysqli_query($con,$sql);
$row = mysqli_fetch_array($result);
echo $row[0];