MySQL 8.0

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create table animal (id int primary key, animal varchar(64))
select 1 id, 'cat' animal
union all
select 2, 'dog'
create table body (id int primary key, animal_id int, name varchar(64), cnt int)
select 1 id, 1 animal_id, 'head' name, 1 cnt
union all
select 2, 1, 'paw', 4
union all
select 3, 2, 'head', 1
union all
select 4, 2, 'paw', 4
union all
select 5, 2, 'ear', 2
create table ability (id int primary key, animal_id int, name varchar(64), val int)
select 1 id, 1 animal_id, 'run' name, 10 val
union all
select 2, 1, 'jump', 5
union all
select 3, 2, 'run', 10
union all
select 4, 2, 'jump', 2
union all
select 5, 2, 'defence', 100
select JSON_OBJECTAGG(cat, prop) description
from (select id, animal prop, 'animal' cat
      from animal
union all
      select animal_id, JSON_OBJECTAGG(name, cnt) prop, 'body' cat
      from body
      group by animal_id
union all
      select animal_id, JSON_OBJECTAGG(name, val) prop, 'ability' cat
      from ability
      group by animal_id) total
group by id


description


{"body": "{"paw": 4, "head": 1}", "animal": "cat", "ability": "{"run": 10, "jump": 5}"}

{"body": "{"ear": 2, "paw": 4, "head": 1}", "animal": "dog", "ability": "{"run": 10, "jump": 2, "defence": 100}"}