PHP - While Loops, Tags And Dysfunctional Search Scripts.

So today I thought I'd try my hand at building a nice little search script for my site in progress. I haven't had any real success with this previously, but I'm trying to amend that.

I've produced this search script which should take the user's search request, call information from the 'ad' database - it contains all the advertisement information (name,images,tags etc.) - compare it to the 'name' and 'tag' fields of the database and display any matching results. I'm here of course because this is not working as planned. There are no errors popping up, the script just isn't displaying results when it should be. Searches that use keywords featured in tags do not produce any results. Anyone have any idea why this script doesn't produce any results?

SQL 'ad' Table:

Code: [Select]
CREATE TABLE IF NOT EXISTS `ad` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(300) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `text` varchar(600) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `apic` varchar(300) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `usr` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `tags` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  PRIMARY KEY (`id`),
  KEY `usr` (`usr`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=9 ;
PHP script:

Code: [Select]
<?php include 'connect.php'; 

  session_start();
  $_SESSION['username']; 
  
  if(!(isset($_SESSION['login']) && $_SESSION['login']!= " ")){
       header("Location: login.php");
   }
   
  $username = $_SESSION['username'];
  $tablename = 'ad';
  
  $search = stripslashes($_POST['search']);
  $search = mysql_real_escape_string($search);
  $search = trim($search);
  
  if (isset($search))
     {
 
 $sql = " SELECT * FROM $tablename";
 $result = mysql_query($sql) or die (mysql_error());
 
 }
 
  else header("Location:search_err.php");
  
  if (mysql_num_rows($result) <0)
  {
   header("Location:search_err.php");
   }
   
  $ad_data = "Results for: " .$search."";
  
  $x=1;
  while($ads = mysql_fetch_array($result) && $x <= mysql_num_rows($result))
  {
    $ad_name = $ads['name'];
    $ad_text = $ads['text'];
    $ad_pic = $ads['apic'];
    $ad_usr = $ads['usr'];
    $ad_tags = $ads['tags'];
  
    if(stristr($ad_name, $search))
{
  $ad_data = "<a href = ad_page.php>". $ad_name ."</a>";
  $xi=1;
}
else
{
  $xi=0;
}
    
if(isset($xi) && $xi == 1)
{
  $ad_tags_exp = explode(',',$ad_tags);
  $fi = 0;
  
  while($fi = 0)
  {
    if($ad_tags_exp[$fi] == $search)
{
$fi = 1;
$ad_data = $ad_data = "<a href = ad_page.php>". $ad_name ."</a>";
}
  }
    }
$x++;
   }
   
   echo $ad_data;
?>