How to generate a unique random number in a MySQL db

Question

I'm creating a volunteer and also a separate vendor application form for an airshow. The volunteer and vendor info is stored in separate tables in a MySQL db, one row per volunteer or vendor. There will be about 100 volunteers and 50 vendors. When the application is submitted it should immediately be printed by the applicant, then signed and mailed in. This past year we had problems with some people who didn't immediately print their application so I'd like to still give them the option to immediately print but also send them an e-mail with a link to their specific row in the MySQL db. I have an autoincrement field as the primary key for each table, but I think sending this key to the applicant in an e-mail would be too easy for them to guess another id and access other people's info.
I'm thinking I should add a column to each table which would contain a unique random number and I would then send this key in the e-mail to the applicant. So, can anyone suggest a simple way to do this or suggest a better way of giving the applicant a way to access their own application and no-one elses after they have submitted their form?
Thanks all.
Tony Babb

Answer 1

Thanks so much, that was very helpful. I added the code you suggested to create and display the random number - I called it "vollink" and that worked fine. Then I added the hidden field toward the bottom of the form - it shows at line 311 when I do a "View Source in Int Explorer and then tried adding the code to add it to the table and when I tested it failed with "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1" . The test version of the page is here www.hollisterairshow.com/volunteerapp2.php . The changes I made to add it to the table is shown below , I must be missing something blindingly obvious, if you could suggest a fix I'd really appreciate it. I did add the field to the MySQL table also.
Thanks again
Tony
$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO volunteers (firstname, lastname, email, thursday, friday, saturday, sunday, monday, activity, talents, specialrequests, tshirt, phone, street, city, st, zip, updatedby, vollink) VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, $s)",
                       GetSQLValueString($_POST['firstname'], "text"),
                       GetSQLValueString($_POST['lastname'], "text"),
                       GetSQLValueString($_POST['email'], "text"),
                       GetSQLValueString($_POST['thursday'], "text"),
                       GetSQLValueString($_POST['friday'], "text"),
                       GetSQLValueString($_POST['saturday'], "text"),
                       GetSQLValueString($_POST['sunday'], "text"),
                       GetSQLValueString($_POST['monday'], "text"),
                       GetSQLValueString($_POST['activity'], "text"),
                       GetSQLValueString($_POST['specialtalents'], "text"),
                       GetSQLValueString($_POST['specialrequests'], "text"),
                       GetSQLValueString($_POST['tshirt'], "text"),
                       GetSQLValueString($_POST['phone'], "text"),
                       GetSQLValueString($_POST['street'], "text"),
                       GetSQLValueString($_POST['city'], "text"),
                       GetSQLValueString($_POST['st'], "text"),
                       GetSQLValueString($_POST['zip'], "text"),
        GetSQLValueString($_POST['vollink'], "text"),
                       GetSQLValueString($_POST['lastname'], "text"));
  mysql_select_db($database_adminconnection, $adminconnection);
  $Result1 = mysql_query($insertSQL, $adminconnection) or die(mysql_error());