Untitled

Pl/SQL - oracle 9i
SELECT COUNT(DISTINCT cust#)
  FROM customer a, car b
 WHERE a.transaction# = b.transaction#
   AND b.model# = 'HONDA'
     AND NOT EXISTS
     (
        SELECT 1
          FROM customer c, car d
         WHERE c.transaction# = d.transaction#
             AND d.model# = 'NISSAN'
             AND c.cust# = a.cust#
     )

SELECT COUNT(DISTINCT cust.CUST#) AS COUNT FROM CUSTOMER cust INNER JOIN CAR car ON
cust.TRANS#=car.TRANS# WHERE CAR_MODEL#='HONDA'
AND NOT EXISTS
(SELECT COUNT(1) FROM CUSTOMER inner_cust INNER JOIN CAR inner_car ON
inner_cust.TRANS#=inner_car.TRANS#
AND inner_cust.CUST#=inner_car.CUST# WHERE inner_car.CAR_MODEL#='NISSAN')