SELECT DISTINCT
  t2.customer_id AS customer_id
FROM table t1
LEFT JOIN table t2 ON t2.customer_id = t1.customer_id
                  AND t2.date_from BETWEEN t1.date_from AND t1.date_to

SELECT last_name, license_number
FROM cars_has_customers AS t1
JOIN customers ON t1.customers_id= customers.id
WHERE EXISTS 
         (
           SELECT NULL
             FROM cars_has_customers AS t2
            WHERE t1.customers_id = t2.customers_id
              AND t1.date_to >= t2.date_from
              AND t2.date_to >= t1.date_from
              AND t1.cars_id != t2.cars_id
         )
  GROUP BY license_number, last_name
  ORDER BY last_name, license_number ;