SELECT NQ.title, COUNT(1) AS page_contributors

FROM

(

    SELECT REPLACE(P.page_title,'_',' ') AS title, A.actor_name AS actor, COUNT(1) AS edits 

    FROM ukwiki_p.revision R

      JOIN ukwiki_p.page P ON R.rev_page=P.page_id

      JOIN ukwiki_p.actor A ON R.rev_actor=A.actor_id

    WHERE R.rev_timestamp > 20191001000000

      AND P.page_namespace = 0

    GROUP BY A.actor_name, P.page_title

    ORDER BY edits DESC

) AS NQ

GROUP BY title

ORDER BY page_contributors DESC

LIMIT 20