SQL JOIN WITH GROUP CONCAT

SELECT booking_details.booking_id,GROUP_CONCAT(ud.model_number) as model,
GROUP_CONCAT(sp.requestd_spare) as spare_part
FROM booking_details 
LEFT JOIN booking_unit_details ud ON ud.booking_id = booking_details.booking_id LEFT JOIN spare_part sp ON sp.booking_id = booking_details.booking_id 
GROUP BY booking_details.booking_id

In above query i want spare_part value should be more then 1 only if sp table has more then 1 row, it should not contain multiple value if ud has more then 1 row