JSON Object building in SQL. Should I build the objects in SQL or in my Application?

I am generating JSON objects via a SQL query, however, I am thinking that I should be building the objects in my application logic (node.js) instead. Given the following structure and query; what would be a way to query the data so that it could easily be transformed?

For full example @see http://ift.tt/1EhUkHU

** Expected Output JSON **

{
    id: <int>
    parent_comment_id: <int>
    content: <string>
    created: <int>
    user: {
        id: <int>
        username: <string>
        name_first: <string>
        name_last: <string>
    }
    tags: {
        <string>:<int|string>
    }
}

Table Structure

CREATE TABLE `comment` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `parent_comment_id` bigint(20) unsigned DEFAULT NULL,
  `user_id` bigint(20) unsigned NOT NULL,
  `content` text CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci,
  `created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB
;
CREATE TABLE `comment_tag` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `comment_id` bigint(20) unsigned NOT NULL,
  `ref_type` varchar(64) NOT NULL,
  `ref_text` varchar(255) DEFAULT NULL,
  `ref_id` bigint(20) unsigned DEFAULT NULL,
  `created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB
;
CREATE TABLE `user` (
 `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(64) NOT NULL UNIQUE KEY,
  `name_first` varchar(64) NOT NULL,
  `name_last` varchar(64) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB
;

Current Query

SELECT
  `c`.`id` AS `id`,
  `c`.`parent_comment_id` AS `parent_comment_id`,
  `c`.`content` AS `content`,
  `c`.`created` AS `created`,
  CONCAT('{', 
    CONCAT('"id": "', `u`.`id`, '",'),
    CONCAT('"username": "', `u`.`username`, '",'),
    CONCAT('"name_first": "', `u`.`name_first`, '",'),
    CONCAT('"name_last": "', `u`.`name_last`, '"'),
  '}') AS `user`,
  IF(`t`.`id` IS NULL, NULL, CONCAT('{',GROUP_CONCAT( 
    CONCAT_WS(
      ':',
      CONCAT('"',`t`.`ref_type`, '"'),
      `t`.`ref_id`,
      IF(`t`.`ref_text` IS NOT NULL, CONCAT('"',`t`.`ref_text`,'"'), NULL)
    )), '}')) AS `tags`
FROM `comment` AS `c`
JOIN `user` AS `u`
ON `c`.`user_id` = `u`.`id`
LEFT JOIN `comment_tag` AS `t`
ON `c`.`id` = `t`.`comment_id`
GROUP BY `c`.`id`