Configuration file:
<code lang="PHP">
<?php

  # Configuration
  $config['sql']['host'] = "localhost";
  $config['sql']['user'] = "root";
  $config['sql']['pass'] = "";
  $config['sql']['base'] = "test";

?>
</code>

Class file:
<code lang="PHP">
<?php
  class db_mysql {

    var $link;
    var $host;
    var $user;
    var $pass;
    var $base;

    function db_mysql() {
      global $config;
      $this->host = $config['sql']['host'];
      $this->user = $config['sql']['user'];
      $this->pass = $config['sql']['pass'];
      $this->base = $config['sql']['base'];
    }

    public function connect() {
      $this->link = mysql_connect($this->host, $this->user, $this->pass) or die("<b>Error:</b> Connection to database server cannot be established.");
      mysql_select_db($this->base, $this->link)or die("<b>Error:</b> Connection to database cannot be established.");
    }

    public function close() {
      mysql_close($this->link);
    }

    private function query($query) {
      $result = mysql_query ($query, $this -> link);
      return $result;
    }

    public function strip($string) {
      # For use in querystring - prevents SQL injections
      return "'" . mysql_real_escape_string($string, $this->link) . "'";
    }

    public function list_assoc($query) {
      $results = array();

      # Querying database
      $resource = $this->query($query);

      # Stacking all results in one array
      while ($row = @mysql_fetch_assoc ($resource)) {
        $results[] = $row;
      }

      @mysql_free_result($resource);
      return $results;
    }

    public function row_assoc($query) {

      # Querying database
      $resource = $this->query($query);

      # Fetching result
      $result = @mysql_fetch_assoc ($resource);

      @mysql_free_result($resource);
      return $result;
    }

    public function update($table, $vals, $where) {
      $result = $this->query("UPDATE " . $table . " SET " . $vals . " WHERE " . $where);
      return $result;
    }

    public function insert($table, $vals) {
      $result = $this->query("INSERT INTO " . $table . " SET " . $vals);
      return $result;
    }

  }
?>
</code>

Usage:
<code lang="PHP">
<?php

  $db = new db_mysql();
  $db->connect();

  # List
  $users = $db->list_assoc("SELECT username FROM users ORDER BY username ASC");
  foreach ($users as $user) {
    echo($user['username'] . "<br />");
  }

  # One row
  $user = $db->row_assoc("SELECT username FROM users WHERE id = " . $db->strip($_GET['id']));
  echo($user['username']);

  # Insert
  $db->insert("users", "username = " . $db->strip($_GET['username']) . ", password = " . $db->strip($_GET['password']));

  # Update
  $db->update("users", "username = " . $db->strip($_GET['username']), "id = " . $db->strip($_GET['id']));

  $db->close();

?>
</code>