check if email already exists in database jquery +php - php

Question

Hy I'm trying to validate the email address in a registration form. I want to check if the address exists in the database;
i have the following function:
function validateEmailRepeat(){
// check if email exists in the database;
var emailVal = $('#email').val();
// assuming this is a input text field
$.post('check_email.php', {'email' : emailVal}, function(data) {
if(data==1)
{
email.addClass("error");
emailInfo.text("Adress exists");
emailInfo.addClass("error");
dataExist=1;
}
else {
email.removeClass("error");
emailInfo.text("Valid adress");
emailInfo.removeClass("error");
dataExist=0;
}
});
if(dataExist==1)
return false;
else
return true;
}
the check_email.php looks like this:
require_once('db.php');
if (isset($_POST['email'])){
$email=mysqli_real_escape_string($con,$_POST['email']);
$sql = "SELECT * FROM users WHERE `username`='".$email."'";
$select=mysqli_query($con,$sql) or die("fail");
$row = mysqli_num_rows($select);
if ($row >0) {
echo 1;
}else echo 0 ;
}
else
echo "post error";
i'm new at this . So don't be to tough. thanks in advance.
LE:Sorry ! i forgot the question...
the problem is that my function returns true if I define var dataExist outside of the function form $.post
and if i let it like it is now in the function I get "dataExist is not defined " error and returns true
Le: the PHP returns the expected 1 and 0 just the way i wanted..
LE:
seems like defining the
var dataExist=0;
outside the function validateEmailRepeat() resolved the issue.
if there's another way more elegant please tell me because this seems a little stupid to me.

Answer 1

The problem is you cannot return the value into the called function, because ajax work asynchronously.
function validateEmailRepeat(){
// check if email exists in the database;
var emailVal = $('#email').val();
// assuming this is a input text field
$.post('check_email.php', {'email' : emailVal}, function(data) {
if(data==1){
email.addClass("error");
emailInfo.text("Adress exists");
emailInfo.addClass("error");
dataExist=1;
}else{
email.removeClass("error");
emailInfo.text("Valid adress");
emailInfo.removeClass("error");
dataExist=0;
}
$('#some_input').val(dataExist);
validateUserName();
});
}
function validateUserName() {
var input = $('#some_input').val();
if (input) {
alert("This username is already taken");// whatever
} else {
// whatever
}
};

Answer 2

You are comparing the username with the email address. Is this how your DB works?
$sql = "SELECT * FROM users WHERE username='".$email."'";
I bet you have a field in your database for the email itself, otherwise i suggest you do this. The query should look like this:
$sql = "SELECT * FROM users WHERE email = '".$email."'";
Without the single quotes for the column.