Update record if exists...Insert if not

[esiason14]

I'm parsing my pages to find all id's. What I want to do is: if the id already exists in my db then I want to update it...if not I want to insert a record. How can I go about doing that. Any help would be appreciated. Thanks!!

foreach ($url as $value) 
      {
          $base = "http://www.mypage.com/whatever";
          $getit = "".$base."$value";
      	  $input = file_get_contents("$getit");	 
preg_match_all('@<a href="/whatever/([A-Za-z0-9-]+)">(.*?), (.*?)</a>@', $input, $matches);


  for($i=0;$i<40;$i++)
	  {	
     $sql3 = "SELECT id from mlbplayers where id=".$matches[1][$i].""; 
	        while ($row3 = mysql_fetch_assoc($result3)) 
	  {			
			$pid = $row3["id"];
	  } 
echo "$sql3<br />";
      }
	  }

[NogDog]

See the on duplicate key option of the insert statement.