为什么这个PHP mysqli fetch适用于第一次运行，但不适用于循环？

function GetMessageFromDB(&$id, &$phone, &$message)
{
  $found = FALSE;

  $stmt = $this->db->prepare('SELECT id, phone, message FROM messages WHERE count <= 0 LIMIT 1');
  $stmt->execute();
  $stmt->bind_result($id, $phone, $message);
  $found = $stmt->fetch();
  $stmt->close();

  echo("GetMessageFromDB: ... ");

  if ($found) {
    echo("found
");
    $this->db->query("UPDATE messages SET `count`=count+1 WHERE `id`=$id");
    $this->db->commit();
  } else {
    echo("not found
");
  }

  return $found;
}

function SendAll()
{
  while (true) {
    $found = $this->GetMessageFromDB($id, $phone, $message);
    while ($found) {
    # $this->DoSomething($phone, $message);
      $found = $this->GetMessageFromDB($id, $phone, $message);
    }
    echo("sleep ...
");
    sleep(10);
  }
}

When I run SendAll(), results are correctly retrieved from the DB one by one. Later, when all records are updated (count from 0 to 1), I update the database record via Sequel Pro (count from 1 to 0). The strange thing is, the program keeps showing not found in the sleep loop.

However, if I ctrl-c the program and restart. Records are found again. What's wrong in my code?

Database connection setup:

  $this->db = new mysqli('127.0.0.1', 'username', 'password', 'sendmsg');
  $this->db->autocommit(FALSE);

$found = $stmt->fetchAll();

Try this