複数コネクションを持つ場合。こんな感じかなぁ･･･

db.php

<?php
class DB{
  var $db_encoding="UTF-8";
  var $script_encoding="UTF-8";
  var $db=null;

  #---------------------------
  # constructer
  #---------------------------
  function DB($db=DBNAME,$user=USER,$pass=PASS,$host=HOST){
    # CONNECT MySQL
    if (!($mysql=mysql_connect($host,$user,$pass,true))) {
      die("ERROR: HOST CONNECT FAILED");
    }

    $this->db = $mysql ;

    # CONNECT DB
    if (!(mysql_select_db($db,$this->db))) {
      die("ERROR: DB CONNECT FAILED");
    }
  }

  #---------------------------
  # class method
  #---------------------------
  function exe($stmt){
  # Execute SQL
    if (!($data = mysql_query($stmt,$this->db))) {
      echo mysql_error($this->db)."\n";
      var_dump($stmt);
      return false;
    }
    $result = Array();
    while($tmp = @mysql_fetch_assoc($data)){
      array_push($result,$tmp);
    }
    if( !empty ( $result ) ){
      return $result;
    }else{
      return TRUE;
    }
  }
}