Zkuste tento dotaz
SELECT group_concat(`type`) AS types,user_id
FROM users
WHERE `type` IN('B','C')
group by user_id
HAVING FIND_IN_SET('B',types)>0 && FIND_IN_SET('C',types)>0
SQL Fiddle http://sqlfiddle.com/#!2/8ef8e/2
Zkuste tento dotaz
SELECT group_concat(`type`) AS types,user_id
FROM users
WHERE `type` IN('B','C')
group by user_id
HAVING FIND_IN_SET('B',types)>0 && FIND_IN_SET('C',types)>0
SQL Fiddle http://sqlfiddle.com/#!2/8ef8e/2