title: PHP/MySQL Check If Value Exists, If So-Do Not Insert It
body: <p>I asked that before, but couldn't figure it out.</p>
  
  <p>I have this form:</p>
  
  <pre><code>&lt;?php
  if ( isset ($_REQUEST['fname']{0}, $_REQUEST['lname']{0}, $_REQUEST['mail']{0}, $_REQUEST['url']{0}) ){
     $query = "INSERT INTO table1 (url, fname, lname, mail) VALUES ('".$_REQUEST[url]."', '".$_REQUEST[fname]."', '".$_REQUEST[lname]."', '".$_REQUEST[mail]."')"; 
  $result = mysql_query($query)
  or die ("Query Failed: " . mysql_error());
  }
  else{
     echo "One Of The Values Not Entered Correctly. Please Press Back In Your Browser And Enter The Missing Values.";
  }
  ?&gt;
  </code></pre>
  
  <p>And I would like to know if it is possible for it to check if a url exists in the system before entering it again.</p>