check for duplicate email entry using php - php

Question

I am trying to check for duplicate emails in a form submit.
My php looks like this
$value = $_POST['name'];
$value2 = $_POST['email'];
$value3 = $_POST['address'];
$value4 = $_POST['city'];
$value5 = $_POST['state'];
$value6 = $_POST['zip'];
$value7 = $_POST['primary'];
$value8 = $_POST['secondary'];
$sql = "INSERT INTO fusiodoseOne (`name`, `email`, `address`, `city`, `state`, `zip`, `primary`, `secondary`) VALUES ('$value', '$value2', '$value3', '$value4', '$value5', '$value6', '$value7', '$value8')";
if(!mysql_query($sql)){
die('Error : ' . mysql_error());
}
//
function createUser($email){
$sql = "SELECT count(email) FROM fusiodoseOne WHERE email='$value2'" ;
$result = mysql_result(mysql_query($sql),0) ;
if( $result > 0 ){
die( "There is already a user with that email!" ) ;
}//end if
What am i doing wrong. The duplicate email entries are still going through
The jquery looks like this
$.post("demo.php",$(this).serialize(),function(data){
$('.successMessageHolder').show();
$('.alertMsg').hide();
});

Answer 1

I don't get the createUser() function.
First: You pass $email as a param, but don't use it, i.e. you use $value2 instead which is in global scope and you can't access it unless you pass it as a parameter ($email in your case) or declare global in function body. It seems it should be:
function createUser($email){
$sql = "SELECT count(email) FROM fusiodoseOne WHERE email='$email'" ;
$result = mysql_result(mysql_query($sql),0) ;
if( $result > 0 ){
die( "There is already a user with that email!" ) ;
}//end if
Second: At what point exactly is the function called? This is a definition, but where and how is it used?