PHP: Check if email already exists when running this code -

i have built simple php form allows user send application using following php code:

if($_server['request_method'] == 'post')     {         $host = '###';         $username = '###';         $pass = '###';          mysql_connect($host,$username,$pass);         mysql_select_db("###");          $status    = mysql_real_escape_string($_post['status']);         $firstname = mysql_real_escape_string($_post['firstname']);         $lastname  = mysql_real_escape_string($_post['lastname']);         $email     = mysql_real_escape_string($_post['email']);         $url       = mysql_real_escape_string($_post['url']);          $query = "insert creathive_applications                    values (null,'$status','$firstname','$lastname','$email','$url')";          $result = mysql_query($query) or trigger_error(mysql_error().". query: ".$query);     } 

what want make sure same person doesn't apply twice if email address exists in database show message on form saying "sorry looks you've applied".

here html form, , have added message inside fieldset, need a) show message if email exits or show success message , b) add #membership form url make view jump form on page user see messages. can this? thanks

    <form action="" method="post">                             <fieldset id="membershipform">                     <div id="error"><p>sorry email in use</p></div> <div id="success"><p>thanks application has been sent</p></div>                                 <ul class="clearfix">                                     <li id="li-status">                                         <span>i a:</span>                                         <menu>                                             <li><label for="student"><input type="radio" name="status" id="student" checked="checked" value="graduate" /> graduate</label></li>                                             <li><label for="student2"><input type="radio" name="status" id="student2" value="undergraduate" /> undergraduate</label></li>                                         </menu>                                     </li>                                     <li id="li-firstname">                                         <label for="firstname">first name</label> <input name="firstname" type="text" placeholder="first name" id="firstname" title="first name" />                                     </li>                                     <li id="li-lastname">                                         <label for="lastname">last name</label> <input name="lastname" type="text" placeholder="last name" id="lastname" title="last name" />                                     </li>                                     <li id="li-email">                                         <label for="email">email address</label> <input name="email" type="text" placeholder="email address" id="email" title="email address" />                                     </li>                                     <li id="li-url">                                         <label for="url">url</label> <input name="url" type="text" placeholder="url of you've made" id="url" title="url of you've made" />                                     </li>                                     <li id="li-buttons">                                         <input name="submit" type="submit" value="send application &#9658;" title="send application" />                                     </li>                                 </ui>                             </fieldset>                         </form> 

do select query before insert validate there aren't entries email already:

select creathive_applications email = $email 

if results come back, display message instead of inserting record. can add javascript onload code move form #membershipform if email existed.