Warning: mysql_result() [function.mysql-result]: Unable to jump to row -1 - php

Question

This is my page code:
<?php
$dbhost="****";
$dbname = '****';
$dbusername="********";
$dbpass="*****;
$con = mysql_connect("$dbhost","$dbusername","$dbpass");
mysql_select_db($dbname,$con);
?>
<main>
<table width='100%' align='center'>
<tr align='center'>
<?php
$sql = "SELECT * FROM file ORDER BY data";
$result = mysql_query($sql);
$num = mysql_num_rows($result);
$j = $num - 1;
$fyear = mysql_result($result, $j, "data");
$year = 2005;
while ($year <= $fyear)
{
$sql = "SELECT * FROM file WHERE posizione = 'uila/blindi.php' AND YEAR(data) = ".$year." ORDER BY data";
$result = mysql_query($sql);
$row = mysql_fetch_array($result);
$num = mysql_num_rows($result);
$i = 0;
echo "<td>";
while ($i < $num)
{
$file = mysql_result($result, $i, "pdf");
$name = mysql_result($result, $i, "nome");
$type = mysql_result($result, $i, "type");
$path = mysql_result($result, $i, "posizione");
echo ""?><?php echo $name; ?><br>
<?php
$i++;
}
echo "</td>";
$year++;
}
?>
</tr>
</table>
And this is the page's error:
Warning: mysql_result() [function.mysql-result]: Unable to jump to row -1 on MySQL result index 2 in D:\Inetpub\webs\uilanotiziecom\bindi.php on line 47
The 47th line is : $j = $num - 1;
How can I fix it?

Answer 1

have you tried this? :
if ( $num >= 1 ) {
$j = $num - 1;
}
if your query returns 0 rows you get the error, what you do in that case is up to you

Answer 2

I think the below sql query is returning empty result that is where you are facing the issue.
$sql = "SELECT * FROM file ORDER BY data";
That's why $j value is -1
And FYI,
Please use proper naming conventions and unique variable names as you have used $sql for both the queries