When changing the select box that particular <options>'s value has to pass to PHP variable on same page. everything happening on create_post.php file, Below code is my check box for that values are getting generated from database
<select id="Category" name="Category">
    <?php
      $sql1 = "SELECT DISTINCT(Cat) FROM categories ORDER BY Cat ASC";
      $qry1 = mysql_query($sql1,$link);
    ?>
      <option value="" selected="">Select Category</option>
    <?php
      while ($row1=mysql_fetch_assoc($qry1)) {                                                                   
    ?>
        <option value="<?php echo $row1['Cat']?>"><?php echo $row1['Cat']?></option>
    <?php 
      }
    ?>
</select>
then when changing the select box option that value have to print on same page.
<?php
  echo "<pre>";
  print_r($_REQUEST);
  echo "</pre>";
  if (isset($_REQUEST['Catgy'])) {
  $mainCat = $_REQUEST['Catgy'];
  echo $mainCat;
  }
?>
Sending select box value through ajax to same page.
$(document).ready(function() {
 $('#Category').change(function(){
   var Category = $(this).find('option:selected').attr('value');
   $.ajax({
     url:'create_post.php',
     data:{'Catgy':Category},
   });
    });
});
Out put is an empty array for print_r and nothing for echo. How to pass select box values when changing to PHP variable on same page?
