session_set_save_handler()中write使用的有关问题

{$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;
    }