[thelist] PHP/MySQL help required

[Dave Stevens]

actually sat down to do some of my ALevel Computing project tonight, ended
up getting driven crazy by this little bit:

basically, I want the script to compare $password (a variable taken from a
text box on a form) with "password" (a row in my customers table) and if
they are the same, put out the relevant code as stated. However, all I get
is:

Warning: Supplied argument is not a valid MySQL result resource in
/home/sites/site108/web/mrw/customers/login.php on line 18

here is the main part of the code:

$sql = "SELECT * FROM customers WHERE username=$username";

        $result = mysql_query($sql);

        $myrow = mysql_fetch_array($result);

 if ($password == $myrow["password"]) {
          $currentuser = $username;
          printf("Welcome back, %s. You can now order from our <a
href=\"../catalogue.php\">catalogue</a>.", $currentuser);

          } else {
          echo "incorrect password.";
          }

disclaimer: I am very new to PHP and MySQL, and as such this code will no
doubt make some people here cringe...sorry!
many thanks in advance for any help!
dave stevens