Learning PHP, MySQL, and JavaScript

rncheckuser.php

To go with rnsignup.php, here’s Example 20-7, rncheckuser.php, the program that looks up a username in the database and returns a string indicating whether it has already been taken. Because it relies on the functions sanitizeString and queryMysql, the program first includes the file rnfunctions.php.

Then, if the $_POST variable 'user' has a value, the function looks it up in the database and, depending on whether it exists as a username, outputs either “Sorry, already taken” or “Username available.” Just checking the function mysql_num_rows against the result is sufficient for this, as it will return 0 for not found, or 1 if it is found.

The HTML entity ← is also used to preface the string with a little left-pointing arrow.

Example 20-7. rncheckuser.php

<?php // rncheckuser.php
include_once 'rnfunctions.php';

if (isset($_POST['user']))
{
    $user = sanitizeString($_POST['user']);
    $query = "SELECT * FROM rnmembers WHERE user='$user'";

    if (mysql_num_rows(queryMysql($query)))
        echo "<font color=red>&nbsp;&larr;
             Sorry, already taken</font>";
    else echo "<font color=green>&nbsp;&larr;
             Username available</font>";
}
?>