Stačí použít následující:
SELECT DISTINCT subscriber.*
FROM subscriber
LEFT OUTER JOIN purchase
ON (subscriber.email = purchase.email and purchase.product_id = 1)
WHERE purchase.product_id IS NULL
Stačí použít následující:
SELECT DISTINCT subscriber.*
FROM subscriber
LEFT OUTER JOIN purchase
ON (subscriber.email = purchase.email and purchase.product_id = 1)
WHERE purchase.product_id IS NULL