Question

I am doing a inventory system for someone. I want to be able to click on a link in the table header and cause it to sort by PN and ASC. Then if I click PN again, by DESC. But I also want to order it by description and do the same thing. Here is my code so far. I cannot figure out how to let it swap directions (ASC, DESC) easily.

            if (!isset($cd))
        {
            $cd = 0;
        }
        if (isset($_SESSION['direction']) && $cd == 1)
        {
            if ($_SESSION['direction'] == 'DESC')
            {
                $_SESSION['direction'] = 'ASC';
                $cd = 0;
            } elseif ($_SESSION['direction'] == 'ASC') 
            {
                $_SESSION['direction'] = 'DESC';
                $cd = 0;
            }
        } else
        {
            $_SESSION['direction'] = 'ASC';
        }
        if (isset($_REQUEST['sort']))
        {
            if ($_REQUEST['sort'] == 'pn')
            {
                $sql=mysql_query("select * from inventory ORDER BY pn {$_SESSION['direction']}");
            } elseif ($_REQUEST['sort'] == 'description') {
                $sql=mysql_query("select * from inventory ORDER BY description {$_SESSION['direction']}");
            } elseif ($_REQUEST['sort'] == 'wholesale') {
                $sql=mysql_query("select * from inventory ORDER BY wholesale {$_SESSION['direction']}");
            } elseif ($_REQUEST['sort'] == 'list') {
                $sql=mysql_query("select * from inventory ORDER BY list {$_SESSION['direction']}");
            } elseif ($_REQUEST['sort'] == 'stock') {
                $sql=mysql_query("select * from inventory ORDER BY stock {$_SESSION['direction']}");
            } elseif ($_REQUEST['sort'] == 'location') {
                $sql=mysql_query("select * from inventory ORDER BY location {$_SESSION['direction']}");
            }
        } else {
            $sql=mysql_query("select * from inventory ORDER BY pn {$_SESSION['direction']}");
        }      
        echo "<center><table class=\"myTable\">
        <th><a href=\"inventory.php?mode=list&sort=pn\">PN</a></th><th><a href=\"inventory.php?mode=list&sort=description\">Description</a></th><th><a href=\"inventory.php?mode=list&sort=wholesale\">Wholesale</th><th><a href=\"inventory.php?mode=list&sort=list\">List</th><th><a href=\"inventory.php?mode=list&sort=stock\">Stock</th><th><a href=\"inventory.php?mode=list&sort=location\">Location</th><th>Links</th>";
        while ($result=mysql_fetch_array($sql))
        {
            echo "<tr><td>{$result['pn']}</td><td>{$result['description']}</td><td>{$result['wholesale']}</td><td>{$result['list']}</td><td>{$result['stock']}</td><td>{$result['location']}</td><td>[<a href='inventory.php?mode=edit&id={$result['id']}'>Edit</a>]  [<a href='inventory.php?mode=delete&id={$result['id']}'>Delete</a>]  [<a href='orders.php?mode=list_c&id={$result['id']}'>View Orders</a>]</tr>";
        }
        echo "</table></center>";

Answer 1

OMG.

Look at this much shortened code of what You have:

$sort_column = 'description'; // the default
$sort_dir = 'DESC'; // the default

$columns = array('pn', 'description', 'wholesale', 'name', 'list', 'stock', 'location');

if (isset($_GET['dir']) && in_array($_GET['dir'], array('ASC', 'DESC'))) {
    $sort_dir = $_GET['dir'];
}
if (isset($_GET['sort']) && in_array($_GET['sort'], $columns))
    $sort_column = $_GET['sort'];
}

$sql = "select * from inventory ORDER BY {$sort_column} {$sort_dir}";

$result = mysql_query($sql);

?>

<center><table class="myTable">
    <th><a href="inventory.php?mode=list&sort=pn<?php if($sort_column == 'pn' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">PN</a></th>
    <th><a href="inventory.php?mode=list&sort=description<?php if($sort_column == 'description' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">Description</a></th>
    <th><a href="inventory.php?mode=list&sort=wholesale<?php if($sort_column == 'wholesale' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">Wholesale</th>
    <th><a href="inventory.php?mode=list&sort=list<?php if($sort_column == 'list' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">List</th>
    <th><a href="inventory.php?mode=list&sort=stock<?php if($sort_column == 'stock' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">Stock</th>
    <th><a href="inventory.php?mode=list&sort=location<?php if($sort_column == 'location' && $sort_dir == 'DESC') echo '&dir=ASC'; ?>">Location</th><th>Links</th>

<?php while ($result=mysql_fetch_array($sql)) { ?>
    <tr>
        <td><?=$result['pn']?></td>
        <td><?=$result['description']?></td>
        <td><?=$result['wholesale']?></td>
        <td><?=$result['list']?></td>
        <td><?=$result['stock']?></td>
        <td><?=$result['location']?></td>
        <td>[<a href="inventory.php?mode=edit&id=<?=$result['id']?>">Edit</a>]  [<a href="inventory.php?mode=delete&id=<?=$result['id']?>">Delete</a>]  [<a href="orders.php?mode=list_c&id=<?=$result['id']?>">View Orders</a>]</td>
    </tr>
<?php } ?>

</table></center>

But You should not use mysql_* functions, learn PDO or at least mysqli_*