EXPLAIN config;
+-------------+--------------+------+-----+---------+-------+
| FIELD       | Type         | NULL | Key | DEFAULT | Extra |
+-------------+--------------+------+-----+---------+-------+
| configUser  | INT(11)      | NO   |     | 0       |       |
| configVar   | VARCHAR(255) | NO   |     | NULL    |       |
| configValue | VARCHAR(255) | NO   |     | NULL    |       |
+-------------+--------------+------+-----+---------+-------+
 
 SELECT * FROM config;
+------------+----------------+-------------+
| configUser | configVar      | configValue |
+------------+----------------+-------------+
|          0 | streamsPerPage | 30          |
|          1 | streamsPerPage | 10          |
+------------+----------------+-------------+

The problem this is when you're trying to get the config value from the database for a user and the value is set, if you don't want to run two queries that is:

SELECT * FROM config WHERE configUser = 0;
SELECT * FROM config WHERE configUser = 4384;

function getConfig($uid = 0) {
  $ids = array("0", => 0, "1", $uid);
  $ids = array_unique($ids);
  foreach ( $ids as $id ) {
   $sql = "select * from config where configUser = $id";
   $data = executeSql($sql);
   foreach ( $data as $q ) {
     $return[$q[configVar]] = $q[configValue];
   }
  }
 return $return;
}

Could be used, but you do want a more elegant way, right?

SELECT
  *
 FROM
  config
 WHERE
  configUser =
   (SELECT
    max(configUser)
   FROM
    config
   WHERE
    configUser = 4384
   OR
    configUser = 0);

Could also work, but sub-queries are CPU hoggers. So what I came up with (with some help from my friends):

SELECT
 config.configVar,
 IFNULL(userconfig.configvalue, config.configvalue) AS configValue
FROM
 config LEFT JOIN config as userconfig
    on
     (userconfig.configVar = config.configVar AND userconfig.configuser=4384)
  WHERE
    config.configuser=0";

This gives us the following code:

function getConfig($uid = 0) {
  $sql = "select
                 config.configVar,
                 ifnull(userconfig.configvalue, config.configvalue) as configValue
          from
                 config
          left join
                 config as userconfig on (userconfig.configVar = config.configVar and userconfig.configuser=$uid)
          where
                 config.configuser=0";
  $data = executeSql($sql);
  foreach ( $data as $q ) {
    $return[$q[configVar]] = $q[configValue];
  }
 return $return;
}

function checkname($string, $allowed) {
$allowed = "/[$allowed]/s";
$string = preg_replace($allowed, "", $string);
if ( $string )
return FALSE;
else
return TRUE;
}

So what you'll do is remove all allowed characters, and if there are any left in the string the user has chosen an invalid username. Ofcourse it's regexp that does the trick. Using the code:

if ( ! checkname($input, "A-Za-z0-9_\.") )
echo "Invalid username!";
else
echo "Ok, lets go!

We're allowing A-Z, a-z, 0-9, underscore and dots in the username.