function reload(form) { var val = $('seltab').getValue();

       new Ajax.Request('Website.php?cat=' +escape(val),
                {
                 method:'get',
                 onSuccess: function(transport){
                   var response = transport.responseText ;
                   $("MyDivDB").innerHTML = transport.responseText ;
                   alert("Success! \n\n" + response);
                   },
                 onFailure: function(){ alert('Something went wrong...') }
                });


    }
</script>
</head>

title author pages

$con = mysql_connect($dbhostname,$dbuserid,$dbpassword);
if(!$con)
{
                       die ("connection failed".mysql_error());
}
$db = mysql_select_db($dbname,$con);
if(!$db)
{
        die("Database is not selected".mysql_error());
}
              $query  ="SELECT * FROM books NATURAL JOIN authors" ;
              $result = mysql_query($query);
if(!$query)
{
       die("Database is not query".mysql_error());
}
while($row = mysql_fetch_array($result,MYSQL_ASSOC))
{

    $title = $row["title"];
    $author = $row["author"];
    $page = $row["pages"];
    echo "<tr>";
    echo "<td>$title</td>";
    echo "<td>$author</td>";
    echo "<td>$page</td>";
    echo "</tr>";
}
print "</table>";
echo "<select id = seltab onchange =  'reload(this.form)'>";
    $querysel = "SELECT title_id,author FROM authors NATURAL JOIN books";
$result1 = mysql_query($querysel) ;
while($rowID = mysql_fetch_assoc($result1))
{
    $TitleID = $rowID['title_id'];
    $author = $rowID['author'];
    print "<option value = $author>$author\n";
    print "</option>";
}
print "</select>";

?>

Wbsite.php