https://hashrocket.com/blog/posts/faster-json-generation-with-postgresql#conclusions

pgsql_query_with_json_responce.sql

WITH messages_ranks AS (
                           SELECT *,
                                  rank() OVER ( PARTITION BY channel_id ORDER BY created_at DESC) AS rank
FROM messages
)
SELECT row_to_json(t)
FROM (
         SELECT channels.id,
                channels.name,
                channels.owner_id,
                (
                SELECT array_to_json(array_agg(row_to_json(messages_arr)))
                FROM (
                         SELECT
                messages_ranks.id,
                    messages_ranks.user_id,
                    messages_ranks.channel_id,
                    messages_ranks.text,
                    messages_ranks.created_at
                FROM users
                LEFT JOIN memberships
                ON users.id = memberships.user_id
                LEFT JOIN channels
                ON channels.id = memberships.channel_id
                LEFT JOIN messages_ranks
                ON messages_ranks.channel_id = channels.id
                WHERE users.id = 'b741c187-d7f5-42a0-ad8f-0eb038a1b2c8'
                AND messages_ranks.rank <= 3
                ORDER BY messages_ranks.created_at DESC
                ) messages_arr
     ) as messages
FROM channels
) t;

/* responce:
{
   "id":"71aeb67e-1c72-435b-a9f8-c20d589aa917",
   "name":"whatever",
   "owner_id":"86c9df47-5c77-4939-bb90-0a6fca8cb4a3",
   "messages":[
      {
         "id":"2bf6663f-a4a7-486e-a70a-e190eb2741d9",
         "user_id":"b741c187-d7f5-42a0-ad8f-0eb038a1b2c8",
         "channel_id":"73bd49d5-e8d1-477f-b10f-e9a51723bb6c",
         "text":"whatever",
         "created_at":"2018-12-07T23:34:37.577097"
      },
      ...
      {
         "id":"0e69d185-472c-4ccb-9d3b-43b0b5c08e0b",
         "user_id":"86c9df47-5c77-4939-bb90-0a6fca8cb4a3",
         "channel_id":"3dc810e5-4e11-4447-847c-e41af8b0214c",
         "text":"whatever",
         "created_at":"2018-12-05T20:59:57.850526"
      }
   ]
}
*/

👻