public function limit($offset = 0, $limit = 10)
{
$offset = intval($offset);
$limit = intval($limit);
$offset < 0 && ($offset = 0);
($limit < 1 || $limit > 5000) && ($limit = 100);
$this->sql['limit'] = "LIMIT {$offset}, {$limit}";
return $this;
}