How do I check database for a value that already exists? - php

Question

I am currently building a signup script for my website. I new to the whole PHP-mySQL interaction bit. Anyway, this is the code I've gotten so far. The problem is that I had added some more code to check if the username already exists in the database, after the form submits it kicks to store.viddir.com/join/signup.php rather than store.viddir.com/login, like I had it. Any pros that can help a novice out? Many thanks
<?php
$submitted = $_POST["submitted"];
if($submitted == 'yes') {
$firstName = $_POST["firstName"];
$lastName = $_POST["lastName"];
$userName = $_POST["userName"];
$password = $_POST["password"];
$confirmPassword = $_POST["confirmPassword"];
$eMail = $_POST["eMail"];
// Kill script if input fields are blank
if ($firstName == '' or $lastName == '' or $userName == '' or $password == '' or $confirmPassword == '' or $eMail == '')
{
die();
}
// Check if passwords match
if ($password != $confirmPassword)
{
die();
}
// Check if password is appropriat length
$passwordLength = strlen($password);
if ($passwordLength < 7 or $passwordLength >30) {
die();
}
/////////////////////////
// Connect to database //
/////////////////////////
$sqlserver = "localhost";
$sqluser = "XXXX";
$sqlpassword = "XXXXXX";
mysql_connect($sqlserver, $sqluser, $sqlpassword) or die(mysql_error());
mysql_select_db("store");
// Check database if username already exists
$newUserName = $userName;
$checkUserName = mysql_query("SELECT userName FROM userInfo WHERE userName = '$newUserName'");
if ($checkUserName) {
die();
}
//////////////////////////
// Insert into database //
//////////////////////////
// Signup time in Unix Epoch
$time = time();
// Human readable date
$date = date("F jS, Y g:i:s A");
$sql = "INSERT into userInfo (firstName, lastName, userName, password, eMail, time, date) VALUES ('$firstName', '$lastName', '$userName', '$password', '$eMail', '$time', '$date')";
//$sqlserver = "localhost";
//$sqluser = "XXXX";
//$sqlpassword = "XXXXXX";
//mysql_connect($sqlserver, $sqluser, $sqlpassword) or die(mysql_error());
//mysql_select_db("store");
mysql_query($sql) or die(mysql_error());
mysql_close();
header("Location: http://store.viddir.com/login");
exit;
}
?>

Answer 1

See mysql_num_rows. You should also look into using PDO or MySQLi
http://php.net/manual/en/function.mysql-num-rows.php
if (mysql_num_rows($query) > 0) {
echo "user already exists";
}

Answer 2

You should do a count in the mysql query and then check if the result is not equal to 0.
Example:
// Check database if username already exists
$newUserName = $userName;
$checkUserName = mysql_query("SELECT COUNT(userName) FROM userInfo WHERE userName = '$newUserName'");
if ( mysql_result($checkUserName, 0, 0) != 0 ) {
die();
}