Sorting a table through an HTML form and PHP?

Question

Basically I'm using an HTML form and PHP to connect to a MySQL database, and I want the user to be able to choose how they want to sort the results from a drop-down menu before the results are actually returned.

Here's my form:

<p>View the complete list of books as sorted by:
<form action="usersort.php" method="post">
<select name="sortby"><option value="book_name">Book Title</option>
<option value="author">Author</option></select>
<input type="submit" name="submit" value="Go"></form></p>

And here's my PHP:

<?php
echo '<table align="center" cellspacing="0" cellpadding="5" width="75%"> <tr>
<td align="left"><b><a href="usersort.php?sort=book_name">Book Name</a></b></td>
<td align="left"><b><a href="usersort.php?sort=author">Author</a></b></td>';
require ('mysqli_connect.php');

$sort = (isset($_GET['sortby'])) ? $_GET['sortby'] : 'books';

switch($sort) {
case 'book_name':
$order_by = 'book_name ASC';
break;
case 'author':
$order_by = 'author ASC';
break;
default:
$order_by = 'book_name ASC';
$sort = 'books';
break;
}

$q = "SELECT (book_name) AS name, (author) AS author, (publisher) AS publisher FROM books ORDER BY $order_by";
$r = @mysqli_query ($dbc, $q);
if ($r) {
echo '<table align="center" cellspacing="3" cellpadding="3" width="75%">
<tr><td align="left"><b>Book Name</b></td><td align="left"><b><Author</b></td></tr>';

while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC))
{echo '<tr><td align="left">' . $row['name'] . '</td><td align = "left">' . $row['author'] . '</td><td align = "left">' . $row['publisher'] . '</td></tr>';
}

echo '</table>';

mysqli_free_result($r);

} else {
echo 'The current books could not be retrieved.';

echo '<p>' . mysqli_error($dbc) . '<br><br>Query: ' . $q . '</p>';

}

?>

I assumed that since I named the select value in the HTML form as "sortby" that my PHP would retrieve the value and insert it for "sortby" but whenever I try to access the return through the form, it always just uses the default case in the switch condition? Can someone tell me what I'm doing wrong?

Answer 1

You post the form and get the value by using $_POST Instead of $_GET

Change

$sort = (isset($_GET['sortby'])) ? $_GET['sortby'] : 'books';

to

$sort = (isset($_POST['sortby'])) ? $_POST['sortby'] : 'books';

Answer 2

It's because your form action is set to post rather than get . Your PHP isset is looking for a global $_GET when it should be looking for a $_POST .

The line should be changed to:

$sort = (isset($_POST['sortby'])) ? $_POST['sortby'] : 'books';

You should also clean up the indentation on your switch statement:

switch($sort) {
    case 'book_name':
        $order_by = 'book_name ASC';
        break;
    case 'author':
        $order_by = 'author ASC';
        break;
    default:
        $order_by = 'book_name ASC';
        $sort = 'books';
        break;
}

Answer 3

$sort = (isset($_POST['sortby'])) ? $_POST['sortby'] : 'book_name';  //<<  HERE

switch($sort) {
case 'book_name':
$order_by = 'book_name ASC';
break;
case 'author':
$order_by = 'author ASC';
break;
default:
$order_by = 'book_name ASC';
$sort = 'book_name';   //<< AND HERE
break;
}