protected function pushHint()
    {
        if( $this->hint ) {
            $this->parts[] = $this->hintMode ? : 'USE';
            $this->parts[] = 'INDEX';
            if( is_array($this->hint) ) {
                $this->parts[] = '(' . join(', ', array_map(array($this, 'quoteIdentifierIfNotExpression'), $this->hint)) . ')';
            } else {
                $this->parts[] = '(' . $this->quoteIdentifierIfNotExpression($this->hint) . ')';
            }
        }
    }