Anda dapat mencoba kueri di bawah ini yang berfungsi untuk mendapatkan posting terakhir dari setiap buku
select
b.id,
b.name,
p.content,
p.published_date
from book b
join post p on p.book_id = b.id
left join post p1 on p1.book_id = p.book_id and p1.published_date > p.published_date
where p1.id is null;
ATAU
select
b.id,
b.name,
p.content,
p.published_date
from book b
join post p on p.book_id = b.id
where not exists(
select 1 from post p1
where p.book_id = p1.book_id
and p1.published_date > p.published_date
)