Select count of rows in another table in a Postgres SELECT statement

Question

I don\'t know quite how to phrase this so please help me with the title as well. :)

I have two tables. Let\'s call them A and B. The

Answer 1

I think the comment by @intgr in another answer is so valuable I'm putting forward this as an alternate answer as this method allows you to filter the calculated column efficiently.

SELECT
  a.*,
  COUNT(b.id) AS b_count

FROM a
INNER JOIN b on b.a_id = a.id
WHERE a.id > 50 AND b.ID < 100 -- example of filtering joined tables, optional

GROUP BY a.id
HAVING COUNT(b.id) > 10 -- example of filtering calculated column, optional
ORDER BY a.id