ช่วยดู code นี้ให้หน่อยนะค่ะ

<?php
 $str_server = "localhost";
 $str_username = "root";
 $str_password = "";
 $str_dbname = "test";
 $obj_con = mysql_connect($str_server,$str_username,$str_password)or die("Error to connect to Database");
 mysql_select_db($str_dbname,$obj_con);
 mysql_query("SET NAMES UTF8");
 $str_sql = "SELECT time FROM daytime WHERE time =(SELECT MAX(volt) FROM daytime WHERE day=curdate())";
 $rs = mysql_query($str_sql,$obj_con); 
 $x = mysql_result($rs,0,0);
 $arr = array();
 $arr[0] = $x;
 header("content-type: application/json");
 echo $_GET['callback'].'('. json_encode($arr). ')';
 ?>
 มีปัญหาขึ้นว่า

<br />
<b>Warning</b>:  mysql_result(): Unable to jump to row 0 on MySQL result index 4 in <b>C:xampphtdocs	est2daytime.php</b> on line <b>11</b><br />
<br />
<b>Notice</b>:  Undefined index: callback in <b>C:xampphtdocs	est2daytime.php</b> on line <b>15</b><br />
([false]) 

ควรแก้ไขอย่างไรดีค่ะ

$x = @mysql_result(@mysql_query("
SELECT time FROM daytime WHERE time=(SELECT MAX.............
"),0,0);