select distinct A.id
from A inner join B on B.a_id = A.id
where B.x >= 5 and B.x <= 10;

select A.id
from A
where A.id in (select B.a_id from B where B.x > 5)

select A.id
from A
where exists (select 1 from B where b.x > 5 and b.a_id = a.id limit 1)

SELECT DISTINCT a_id AS id
FROM B
WHERE x >= 5 and x <= 10 ;

SELECT a_id AS id
FROM B
GROUP BY a_id
HAVING MAX(x) >= 5
   AND MIN(x) <= 10 ;

SELECT A.*
FROM A
  JOIN
    ( SELECT a_id
      FROM B
      GROUP BY a_id
      HAVING MAX(x) >= 5
         AND MIN(x) <= 10
    ) AS b
  ON b.a_id = a.id ;