I když můžete spojit několik čísel (v libovolném) do jednoho pole:
SELECT
CONCAT(f_first_name, ' ', f_last_name) as Client_Name,
GROUP_CONCAT(IF(phone_type='work',f_phone_number, NULL)) as Work_Numbers,
GROUP_CONCAT(IF(phone_type='home',f_phone_number, NULL)) as Home_Numbers
FROM clients
JOIN phone
USING (f_id)
WHERE phone_type IN ('home', 'work')
GROUP BY f_id;