public function where($clauses, $statements = null)
    {
        $this->settings['where'] = $clauses;

        if (is_array($this->settings['statements'])) {
            $this->settings['statements'] = array_merge(
                $this->settings['statements'],
                $statements
            );
        } else {
            $this->settings['statements'] = $statements;
        }

        return $this;
    }