PHP form validation

I am currently working on a registration form for my site.

On submit, it runs through a script, which is as follows:

PHP:

<?php
 
if ($_POST) {

// Yes it has been Posted.....and should be full of data from the form
// Need to Validate the data HERE
//

    $firstname=$_POST['firstname'];
    $surname=$_POST['surname'];
    $gender=$_POST['gender'];
    $email=$_POST['email'];
    $contact=$_POST['contact'];
    $gmc=$_POST['gmc'];
    $quals=$_POST['quals'];
    $region=$_POST['region'];
    $system=$_POST['system'];
    $confirm=$_POST['confirm'];

// Check if the Email has been used before
    $query = "SELECT * FROM Locums where email = '$email'";
    $result = mysql_query($query);

// If Error with the Select.....
    if (!$result) {
        echo "Could not access Table";
        die( print_r( mysql_error(),true));
    }

//Select was OK - did it return anything?
    $rows = mysql_num_rows( $result );
    if ($rows === true) {
      die("You have already registered with that e-mail address.");

// *****should Redisplay the page with error.....
}
 
// Nothing returned so OK to create this record in the Locums Table

// Generates random activation code
    $activ_code=uniqid('', true);
    $query="INSERT INTO Locums(firstname, surname, gender, email, contact, gmc, quals, region, system, confirm, uniquecode) VALUES ('$firstname','$surname','$gender','$email','$contact','$gmc','$quals','$region','$system','$confirm','$activ_code')";
    $result=mysql_query($query);

    if (!$result) {
        echo "Error Inserting Record";
        die( print_r( mysql_errors(),true));
    }

?>

All the data inserts in to the table correctly with a unique activation code etc etc but on testing, the email validation does not seem to be working because it allows me to duplicate an email address.

Can anyone help with this?

Thanks.

Excellent, here he is... Mr mlseim, the man I can always count on to solve my woes.

How are you? thanks for the reply by the way, works a treat.
One more thing you may be able to help me with now.

The error appear on the page, but I would like the error to appear just above the form so that the user doesn't have to go back, they can just amend their errors and re-submit.

I did find this bit from a previous code but if you could help me implement this, it would be much appreciated.

PHP:

<?php    
     if(!empty($err))  {
       echo "<div class=\"msg\">";
      foreach ($err as $e) {
        echo "* $e <br>";
        }
      echo "</div>";    
       }
?>

OK, I may just leave this as is and inform the user that they have to click the back button to rectify their errors.
Last thing I wanted to look in to is to highlight the input at the time of them completing the form if they leave it empty, on a previous google search for something else I stumbled across this to put in the input:

PHP:

<?php if($_POST[comments] == ""){ echo "class=\"error\""; ?>

and then just have .error textarea {color: #} in the css, will this work?

Obviously with comments changed to whatever the input name is.

I think this will do for now, It checks for duplicate e-mail addresses and wont submit if there is already one there, and if not it will process the form, it has hints but they will still submit blank if the user leaves them out, hopefully they will see the * and realise they must be completed.

http://tinyurl.com/7qh263p

Just a few more queries regarding this form.
On displaying the form, it looks absolutely fine (see link in previous post) and when submitted correctly, the thank you message is also fine, but if a duplicate email address is entered and the error message displays, it cannot be read because my white background does not show and it is as if the script has just stopped loading, there is no footer, only header and black text with the error.

It is this bit that generates the error:

PHP:

//Select was OK - did it return anything?
    $rows = mysql_num_rows( $result );
// if a row was found, the email has already been used.
    if ($rows > 0) {
      die("You have already registered with that e-mail address. Please click back on your browser to go back and try again.");

// *****should Redisplay the page with error.....
}

Here is the entire thing: http://pastebin.com/CVADqhjZ

Just wondering if its the die before the error message that is stopping the script, considering thats what die does lol

i've changed die to echo and this displays the error with the rest of the page displaying as I want it, except the other bit of text saying thanks for registering displays underneath... I thought that was only supposed to display if the page was loaded NOT from a post, so i'm taking a guess in saying I do need the die somewhere, but the echo can stay where the error is?

I'm still having problems with this form.
I changed the die to a redirect script so that if the email address is already in the database it has this:

PHP:

    $rows = mysql_num_rows( $result );
// if a row was found, the email has already been used.
    if ($rows > 0) {
      header('Location: http://www.siteurl.net/error');
// *****should Redisplay the page with error.....
}

However this doesnt work, all I get is this message:
Warning: Cannot modify header information - headers already sent by (output started at /home/adejones/public_html/locumregister.php:5) in /home/adejones/public_html/locumregister.php on line 105
and the script seems to carry on because after this is has the rest of the "thank you for registering" bla bla, any ideas? anyone?

Thanks