Question

I set up a cron job to run the following script every 30 min, Basically this script selects article info from stories table where field showing=0 And it than counts votes related to that article, the votes are located in votes table. itemname_field in votes table is equal to id field in stories table.
If you need more information on database structure and voting system, I describe it in depth here:
Set a cron job to update article information depending on its vote values

<?php 
    mysql_connect("localhost","username","password") or die (mysql_error("There was an error in connection"));
    mysql_select_db("database") or die (mysql_error("There was an error in connection"));

    $query = "select sum(vt.vote_value) as vote_value, vt.item_name from Votes vt join stories st on st.id = vt.item_name and st.showing = 0 group by vt.item_name";
    $result = mysql_query($query); 
    while($row = mysql_fetch_array($result))
    {
        if($row['vote_value'] > 9) {
            $showing = 1;
        }
        else if($row['vote_value'] < -9) {
            $showing = 2;
        }
        else {
            $showing = 0;
        }
        $query2 = "UPDATE `stories` SET `showing` = $showing WHERE `id` = '".$row['item_name']."'";
        mysql_query($query2); 
    }
?>

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Can anyone suggest the reason, why this script is not working? If everything is alright with script, could it be something in cron job that needs to be done?

EDIT: when I run script in browser it gives the following error:

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL

Which is this line while($row = mysql_fetch_array($result))

Answer 1

The error message you quote means you have an error in your query. Run it though a mysql client to get more info, or echo mysql_error() in php.

In such cases mysql_query() returns boolean false, you can use this for error handling.