PHP/MySQL checking for duplicate content in database

Im loading an xml file with tweets and then adding it a to a Mysql database. Up to this point it works fine but id like to do a basic check on the url field to see if its already added in the database. If its in the database already id like to update the mention count else insert it as a new entry. Its a real newbie question but im struggling to get it working. Heres the code as it stands now:

<?php 

require_once('functions/functions.php');

$dbhost = '****';
$dbuser = '****';
$dbpass = '****';

$conn = mysql_connect($dbhost, $dbuser, $dbpass) or die ('Error connecting to mysql');

if($conn)
 {
    echo "Database Connection 开发者_如何学GoSuccessfull...<br /><br />";
 }

$dbname = '****';
mysql_select_db($dbname) or die('Couldnt connect to database table');

if($dbname)
{
    echo "Database ".$dbname." Selected..<br /><br />";
}

  $tweetmeme = "http://api.tweetmeme.com/stories/popular.xml?category=sports-soccer&count=30" ; 

  $xml = @simplexml_load_file($tweetmeme) or die ("no file loaded") ; 
  if($xml)
  {
    echo "Tweetmeme XML loaded with ".count($xml->stories->story)." stories in the file..<br /><br />";
  }
 if(get_magic_quotes_gpc())
 {
    echo "Magic Quotes is ON<br /><br />";
 }
 $count_insert=0;
 $count_update=0;

 //Select url and id and compare to the url being added
 $url_compare = mysql_query("SELECT id,url FROM ft_tweets");


 if($url_compare)
 {
    //echo_result($url_compare);
    echo mysql_num_rows($url_compare)." rows loaded.<br /><br />";
 }

 $url_compare = mysql_fetch_assoc($url_compare);

foreach($xml->stories->story as $story)
{
    $title=check_input($story->title);


    $url=check_input($story->url);

    $media_type=check_input($story->media_type);

    $created=check_input($story->created_at);

    $url_count=check_input($story->url_count);

    $comment_count=check_input($story->comment_count);

    $excerpt=check_input($story->excerpt);



    $sql = "INSERT INTO ft_tweets (title,url,media_type,created_at,mention_count,comment_count,excerpt) VALUES ($title,$url,$media_type,$created,$url_count         ,$comment_count,$excerpt)";


    $result = mysql_query($sql) or die(mysql_error());
    if($result)
    {
        //echo "added to database<br />";
        $count_insert++;
    }
}
echo $count_insert." Records added to the database<br /><br />";
$search=mysql_query("SELECT * FROM ft_tweets WHERE title LIKE '%liverpool%' OR excerpt LIKE '%lfc%'");
if($search)
{
    echo "<br /><br />Found tweets mentioning Liverpool";
}
//fetch 10 tweets from ft_tweets where liverpool or lfc is in the excerpt or the title and store it in a variable
//echo_result($search);
echo "<br />";
var_dump($search);
echo "<br />";
?>

Seems like you just need to check for a duplicate tweet first.

$sql = "SELECT id FROM ft_tweets WHERE url = '" . mysql_real_escape_string( $url ) . "'";
$duplicate = mysql_query( $sql );
if ( mysql_num_rows( $duplicate ) > 0 ) {
  // some notice about duplicate tweet
  $count_duplicate++;
} else {
  // insert the new
  $sql = "INSERT INTO...";
}

If you set url as Key you can use INSERT ... on DUPLACATE KEY UPDATE sytax.