checking for unique record

[volklskier]

I know that this has been asked before and I have read many posts on the topic but I still can't seem to solve my problem.
I want to check to see if a user has selected a unique username before inserting the record into the database but i keep getting an error message saying Unknown column '$fName' in 'field list'.
I know that there is a column named fName in the database and I have checked the case also. How can i fix this problem.

<?php
include('includes/db.php');

// get input from form
$fName = $_POST['fName'];
$lName = $_POST['lName'];
$email = $_POST['email'];
$username = $_POST['username'];

// error checks the form input
if((!$fName) || (!$lName) || (!$email) || (!$username)) {
    echo('You did not submit the following required information: <br />');
    if(!$fName){
        echo('First Name is a required field. Please enter it below.<br />');
    }
    if(!$lName){
        echo('Last Name is a required field. Please enter it below.<br />');
    }
    if(!$email){
        echo('Email Address is a required field. Please enter it below.<br />');
    }
    if(!$username){
        echo('Username is a required field. Please enter it below.<br />');
    }
    include 'register.html';
    exit();
}

// checks if the user alreay exists
$query = "SELECT username FROM users WHERE username='$username'";
$sql = mysql_query($query) or die(mysql_error().'<br> SQL:'.$query);
$result = mysql_num_rows($sql);

if($result > 0) {
    echo 'The username you have selected has already been used by another member in our database. Please choose a different Username<br />';
        unset($username);
    include 'register.html';
    exit();
}

// insert the user into the database
mysql_query('INSERT INTO users (fName, lName, email, username) VALUES($fName, $lName, $email, $username') or die(mysql_error());
?>

[furtivefelon]

i saw on http://martin.f2o.org/php/login this site that you can add a property to your database that sets username unique.. the table code on that site is:

CREATE TABLE member (   

 id int NOT NULL auto_increment,   

 username varchar(20) NOT NULL default '',    

password char(32) binary NOT NULL default '',    

cookie char(32) binary NOT NULL default '',   

 session char(32) binary NOT NULL default '',    

ip varchar(15) binary NOT NULL default '',    

PRIMARY KEY  (id),    

UNIQUE KEY username (username)  );

i'm not sure if it works.. but it's worth a try 🙂

[devinemke]

try your INSERT statement this way:

mysql_query("INSERT INTO users SET
fName = '$fName',
lName = '$lName',
email = '$email',
username = '$username'") or die(mysql_error());

[volklskier]

that did it. thanks a lot