Question

I’ve got a page that contains a fair few database queries, each appended with or die(). I’m loading this page every 1 second for testing, and on random page loads (it could take two, it could take five, or ten) die() is switched and an error given.

I broke down the script, and managed to isolate the particular offending query, which is:

$fetch = mysql_fetch_assoc($result) or die("Error 3:" . mysql_error());

This particular line is contained within:

if($size > 0) {
    $off_id = array();

    while($row = mysql_fetch_assoc($result)) {
        $off_id[] = $row['off_id'];
    }

    echo '<pre>';
    var_dump($off_id);
    echo '</pre>';

    $rand = rand(0,$size);
    $off_id = $off_id[$rand];

    $query = "UPDATE rotation_data SET hit_counter = hit_counter + 1 WHERE off_id = '{$off_id}'";
    $result = mysql_query($query) or die("Error 1:" . mysql_error());

    $query = "SELECT * FROM offer_data WHERE off_id = '{$off_id}'";
    $result = mysql_query($query) or die("Error 2:" . mysql_error()); 
    $fetch = mysql_fetch_assoc($result) or die("Error 3:" . mysql_error());
    $offer_url = $fetch['url']; $geo_target = $fetch['geo_target']; $blank = $fetch['blank'];

}

Things I noticed:

• No mysql_error() is returned/printed. Only Error 3: is.
• The $off_id array dumps correctly each and every time, so there’s always an $off_id to be used in the previous $result query, and if there wasn’t, that should trigger die() for the $result query instead.

I don’t really understand why this would occur on random page loads, and not all the time, as this perhaps points to it not being a syntax issue, but a load issue?

However, even if it’s a load issue, I don’t understand why that particular query would fail and trigger a die() while the others are fine.

Any help in understanding why this might be, and suggestions of what I could do to fix this would be greatly appreciated!

Answer 1

I am guessing that your query here returns no results:

$query = "SELECT * FROM offer_data WHERE off_id = '{$off_id}'";

The following statement will not return FALSE, just an empty result set into $result.

// No results here this time...
$result = mysql_query($query) or die("Error 2:" . mysql_error()); 

And then you attempt to fetch a row from an empty result resource. This results in FALSE not because of error, but because there are no rows to fetch, and your short-circuit evaluation calls die().

We cannot see where you are setting $size, but it’s possible that you are occasionally reading past the array bounds of $off_id by reaching a random value that is larger than that array.