mysql_fetch_assoc che stampa warning

[rocco.mod]

nuovamente buongiorno ,volevo domandarvi perche una query , stampa un errore warning posto l errore

Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\class_pager-2004-10-22\class.pager.example.php on line 20

e la query:

$array = mysql_query("SELECT * FROM tech  where staffid = staffid ");
$result = mysql_num_rows($array);
if (isset($_GET['page'])) { $page = intval($_GET['page']); } else { $page = 1; }

    $num_results = $result ; //this value should arrive from some database query, like "select count(id) from table_you_want_to_page" 
    $per_page = 1; //number of results to be shown per page
    $query_string = "class.pager.example.php?"; // current file.. 
    echo $num_results ;
    $sql ="SELECT * FROM tech order by staffid asc limit $per_page , $num_result ";
    $query =  mysql_query($sql);
    while($row = mysql_fetch_assoc($query) )
    {
    echo $row['nome'].'-'. $row['cognome'].'-'. $row['username'].'
';
    }
    
    $pr = new pager($num_results, $per_page, $query_string); //building a pager
    $pr->num_results = $result;
    $pr->per_page = $per_page;
    $pr->query_string = $query_string ;
$range = 9; //set the range of page button list
echo $pr->getButList($range); 

    $pr->getPageFrom($page);