How to update date into mysql from external RSS subion?

I want to subscribe a external RSS feed, it with 10 items. and I want to store it into mysql database. When I refresh the page, the database can uptade, the new 10 rss items will replace the older 10.

require_once ('conn.php');
mysql_select_db("my_db", $db);
mysql_query("REPLACE INTO rss (link, title, date, content) VALUES ('".$link."', '".$title."', '".$date."', '".$content."')");

HTML:

I tried Insert and REPLACE, but they all insert new one behind the old.
How to do a update? Thanks.

 

$qid = mysql_query("SELECT title FROM rss WHERE title='$title' AND date='$date' AND content='$content' AND link='$link' LIMIT 1");
if (mysql_num_rows($qid)==0) {
 mysql_query("INSERT INTO rss (link, title, date, content) VALUES ('".$link."', '".$title."', '".$date."', '".$content."')");
}

PHP:

only now inserts if not found

 

Thanks themullet, but
mysql_num_rows(): supplied argument is not a valid MySQL result resource wrong in line: if (mysql_num_rows($qid)==0) {
I replace $qid into $query, but it also alart wrong.
I checked the mysql database, it also insert new rss items when I refresh the page.