WITH

x AS

(SELECT COUNT(sfp.id) AS posti,

        EXTRACT(MONTH FROM sfp.creation_date::date) AS month

FROM stackoverflow.posts AS sfp

WHERE EXTRACT(YEAR FROM sfp.creation_date) = '2008'

GROUP BY month),

 

y AS

(SELECT sfp.id AS postii

FROM stackoverflow.posts AS sfp

INNER JOIN stackoverflow.users AS sfu ON sfp.user_id = sfu.id

WHERE sfu.creation_date :: date BETWEEN '2008-09-01' AND '2008-09-30' AND sfp.creation_date :: date BETWEEN '2008-12-01' AND '2008-12-31')

 

SELECT posti,

       month

FROM x

INNER JOIN y ON x.posti = y.postii

ORDER BY month DESC;