Fix this error Please :(

[RDXZ]

Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in /home/damm/public_html/cost.php on line 9

<?php
$con = mysql_connect("localhost","username","password");
if (!$con)
{
 die('error');
}
$sql = mysql_query("SELECT SUM(`at`) FROM `User`");
$r = mysql_fetch_array($sql);
$total=$r[0];
echo $total;
?>

please guys do something

[softwarefreak]

Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in /home/damm/public_html/cost.php on line 9

<?php
$con = mysql_connect("localhost","username","password");
if (!$con)
{
 die('error');
}
$sql = mysql_query("SELECT SUM(`at`) FROM `User`");
$r = mysql_fetch_array($sql);
$total=$r[0];
echo $total;
?>

please guys do something

are you trying to prove yourself a noob? :D
put ds b4 the the sql query

mysql_select_db("DATABASE_NAME"); 

btw, the php errors lets you know where to correct,
Warning:

mysql_fetch_array() 

expects parameter 1 to be resource, boolean given in
Means $sql is returing

FALSE