CI_Form_validation::is_unique PHP Method

    public function is_unique($str, $field)
    {
        sscanf($field, '%[^.].%[^.]', $table, $field);
        return isset($this->CI->db) ? $this->CI->db->limit(1)->get_where($table, array($field => $str))->num_rows() === 0 : FALSE;
    }