Question

We have a table customer and table car.

customer table is defined as: cust#, transaction#
car table is defined as: transaction#, car model#

car model# can be either nissan, toyota or honda.

what we need to find out is how many distinct customer have bought a honda but not a nissan. there can be multiple records for car model# as a customer can buy 2-3 hondas or nissans.
Transaction # is primary key in car table.

What would be the most cost effective way of doing this?

Answer 1

Try this:

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#
     )