session_set_save_handler()中write使用的有关问题

<?php  require('session.php');  session_start();  $_SESSION['test'] = 1;  echo '<a href="b.php?' . session_name() . '=' . session_id() . '">查看</a>';

<?php  require('session.php');  session_start();

<?php    ini_set('session.save_handler', 'user');    ini_set('session.use_cookies', 0);        session_set_save_handler('open', 'close', 'read', 'write', 'destroy', 'gc');        $link = null;    $expiry = 86400;        function open($save_path, $session_name)    {        //连接数据库    }        function close() {        return true;    }        function read($sessionId) {        global $link;                $sessionId = mysql_escape_string($sessionId);        $time = time();        $sql = "SELECT value FROM session WHERE session_id='{$sessionId}' AND expiry>{$time}";                $result = mysql_query($sql, $link);                if(@$row = mysql_fetch_row($result, $link)) {            return $row[0];        }else {            return '';        }    }        function write($sessionId, $sessionData) {        global $link, $expiry;                $sessionId = mysql_escape_string($sessionId);        $sessionData = mysql_escape_string($sessionData);        $time = time() + $expiry;                $sql = "INSERT INTO session(session_id, value, expiry) VALUES('{$sessionId}', '{$sessionData}', {$time});";        $result = mysql_query($sql, $link);                if($result) {            return true;        }                $sql = "UPDATE session SET value='{$sessionData}', expiry={$time} WHERE session_id='{$sessionId}'";        $result = mysql_query($sql, $link);                    if($result && mysql_affected_rows($link)) {            return true;        }else {            return false;        }    }        function destroy($sessionId) {        global $link;                $sessionId = mysql_escape_string($sessionId);                $sql = "DELETE FROM session WHERE session_id='{$sessionId}';";        $result = mysql_query($sql, $link);                if($result) {            return true;        }else {            return false;        }    }        function gc($maxLifeTime) {        return true;    }