.tip

"The three latest posts for each author" is a join where the right side depends on the left row. That is what LATERAL is for.

SELECT a.name, p.title
FROM authors a
CROSS JOIN LATERAL (
  SELECT title FROM posts WHERE author_id = a.id
  ORDER BY created_at DESC LIMIT 3
) p;

The subquery runs once per author and uses the author's index. Without LATERAL you would rank every post in the table to keep three per author.