Q&A for scientists using computers to solve scientific problems
select count(t1.usersid1) as '<10', count(T2.usersid2) as '10<=...<=20', count(T3.usersid3) as '>20' from (Select users.id as usersid1 from Users left join posts on Users.Id = Posts.owneruserID group by users.id HAVING Count(Posts.id) <10) T1 full JOIN (Select users.id as usersid2 from Users inner join posts on Users.Id = Posts.owneruserID group by users.id HAVING Count(Posts.id) between 10 and 20) T2 ON T1.usersid1 = T2.usersid2 full JOIN ( Select users.id as usersid3 from Users inner join posts on Users.Id = Posts.owneruserID group by users.id HAVING Count(Posts.id) > 20) T3 ON T2.usersid2 = T3.usersid3