//适配目标，规定的接口将被适配对象实现
interface IDatabase
{
  public function connect($host, $username, $password, $database);
  public function query($sql);
}
 
//适配器
class Mysql implements IDatabase
{
  protected $connect;
 
  public function connect($host, $username, $password, $database)
  {
    $connect = mysql_connect($host, $username, $password);
    mysql_select_db($database, $connect);
    $this->connect = $connect;
    //...
  }
 
  public function query($sql)
  {
    //...
  }
}
 
//适配器
class Postgresql implements IDatabase
{
  protected $connect;
 
  public function connect($host, $username, $password, $database)
  {
    $this->connect = pg_connect("host=$host dbname=$database user=$username password=$password");
    //...
  }
 
  public function query($sql)
  {
    //...
  }
}
 
 
//客户端使用
$client = new Postgresql();
$client->query($sql);