linux 中 关于与php 代码的 <php && ?>

<?php
    session_start();
    date_default_timezone_set("PRC");
    include_once("access.php");
    $user_name=$_SESSION[user_name];
    include_once("conn.php");
    include_once("update.php");
    $num_query="select * from ".$table_name." where flag= '1' and user_name='".$user_name."'";
    $num_result=mysql_query($num_query);
    $num=mysql_num_rows($num_result);
    function sel_end($start,$end,$check_table){
        $five_query=$check_table." where end_time<='".$end."' and end_time >'".$start."'";
        //echo $five_query;
        $five_result=mysql_query($five_query);
        $num=mysql_num_rows($five_result);
        while($rows=mysql_fetch_array($five_result))
        {
            echo $rows["host_name"]."  ";
        }
        echo "<br>";
    }
?>