how to avoid duplicating in php - php

Question

i am new in terms of php. i am now creating a simple program which is similar as a login page. may you please help me to do my coding, i have mysql table named user which has 3 column userid, email and password. my primary is userid and it is an auto increment. how can i have code which is, the column email should no duplication or no same email. i have already code for avoiding empty fields i don't know now how to do about the duplication..
here is my sample code:
<?php
if(isset($_POST['submit'])){
$dbhost = 'localhost';
$dbuser = 'root';
$conn = mysql_connect($dbhost, $dbuser);
mysql_select_db('dtr');
if(! $conn ){
die('Could not connect: ' . mysql_error());
}
if(! get_magic_quotes_gpc() ){
$email = addslashes ($_POST['email']);
$password = addslashes ($_POST['password']);
}
else{
$email = $_POST['email'];
$password = $_POST['password'];
}
//validation
if($email == ''){
echo "empty ang email" ?></br><?php ;
return false;
}
if($password == ''){
echo "kailangan may password ka\n" ?></br><?php ;
return false;
}
---------------------->//select * table where username=user
{
$sql = "INSERT INTO user "."(email, password) "."VALUES('$email','$password')";
$retval = mysql_query( $sql, $conn );
}
if(! $retval ){
die('Could not enter data: ' . mysql_error());
}
echo "Entered data successfully\n";
mysql_close($conn);
}
else
{
}
?>
help me plz..

Answer 1

you can try:
$sql = "SELECT userid from users WHERE email = ". $_POST["email"];
if (mysql_num_rows(mysql_query($sql, $con)) >= 1)
{
echo "That email you provided seems to be already used";
return;
}
And please thing about using a different db extension since mysql is deprecated as of PHP V. 5.5. It will give you better security features with binding and prepared statements.

Answer 2

Simply use this, I think it should give u help:
$name = $_POST[name];
$pass = $_POST[pass];
$user = "SELECT * from users WHERE email = '".$email."'";
$result = mysql_query($user);
if(mysql_num_rows($result)>0){
return "$result";
}
else{
mysql_query("INSERT INTO users(email, pass) VALUES ('$email', '$pass')");
}