get count of childs and childs of childs

-- create a table
CREATE TABLE forum (
  forum_id INTEGER PRIMARY KEY,
  name TEXT NOT NULL
);

-- create a table
CREATE TABLE topic (
  topic_id INTEGER PRIMARY KEY,
  forum_id INTEGER NOT NULL,
  name TEXT NOT NULL
);

-- create a table
CREATE TABLE post (
  post_id INTEGER PRIMARY KEY,
  topic_id INTEGER NOT NULL,
  name TEXT NOT NULL
);


INSERT INTO forum VALUES (1, 'Animals');
INSERT INTO forum VALUES (2, 'Technology');


INSERT INTO topic VALUES(1, 1, 'Isnt lion nice?');
INSERT INTO topic VALUES(2, 1, 'Zebras are awesome!');
INSERT INTO topic VALUES(3, 2, 'Dell xps 15 questions');

INSERT INTO post VALUES(1, 1, 'post 1');
INSERT INTO post VALUES(2, 1, 'post 2');
INSERT INTO post VALUES(3, 1, 'post 3');
INSERT INTO post VALUES(4, 2, 'post 4');
INSERT INTO post VALUES(5, 2, 'post 5');
INSERT INTO post VALUES(6, 2, 'post 6');
INSERT INTO post VALUES(7, 2, 'post 7');
INSERT INTO post VALUES(8, 3, 'post 8');


select f.name, count(distinct t.topic_id) as topics_count, count(p.post_id) as posts_count
from forum f
inner join topic t on t.forum_id = f.forum_id
inner join post p on p.topic_id = t.topic_id
group by f.forum_id;