[php] Get the Selected value from the Drop down box in PHP

I am populating a Drop Down Box using the following code.

<select id="select_catalog">
<?php 
$array_all_catalogs = $db->get_all_catalogs();
foreach($array_all_catalogs as $array_catalog){?>
<option value="<?= $array_catalog['catalog_key'] ?>"><?= array_catalog['catalog_name'] ?></option>  

Now how can I get the selected option value using PHP (I have the code to get the selected item using Javascript and jQuery) because I want the selected value to perform a query in database.

Any help will be much appreciated. Thank you very much...

You have to give a name attribute on your <select /> element, and then use it from the $_POST or $_GET (depending on how you transmit data) arrays in PHP. Be sure to sanitize user input, though.

Couldn't you just pass the a name attribute and wrap it in a form?

<form id="form" action="do_stuff.php" method="post">
    <select id="select_catalog" name="select_catalog_query">
    <?php <<<INSERT THE SELECT OPTION LOOP>>> ?>
    </select>
</form>

And then look for $_POST['select_catalog_query'] ?

Posting it from my project.

<select name="parent" id="parent"><option value="0">None</option>
<?php
 $select="select=selected";
 $allparent=mysql_query("select * from tbl_page_content where parent='0'");
 while($parent=mysql_fetch_array($allparent))
   {?>
   <option value="<?= $parent['id']; ?>" <?php if( $pageDetail['parent']==$parent['id'] ) { echo($select); }?>><?= $parent['name']; ?></option>
  <?php 
   }
  ?></select>