rewards the products qualify for - sql

Question

products purchased
--------------------------
bana
bana
bana
stra
kiwi
reward requirements table (related to a rewards table)
reward id, products
----------------------
1,bana
1,bana
1,bana
2,stra
2,bana
3,stra
4,cart
5,bana
5,bana
5,oliv
Can you help me with sql to get rewards
the products purchased qualifies for?
In the case above the reward ids would be:
1
2
3
If there is a better design that would make the solution easier I welcome those as well. I'm using product names for the sake of easier explaining, I hope. (I'll replace with product ids later)

Answer 1

This query will solve your problem.
select r.reward_id
from (
select reward_id, product, count(*) needed
from reward_requirements
group by reward_id, product
) r
left join (
select product, count(*) bought
from products_purchased
group by product
) p on r.product=p.product and p.bought >= r.needed
group by r.reward_id
having count(reward_id) = count(distinct p.product)
order by r.reward_id
To make your design better, you could redo the reward_requirements to have the columns (product, needed) instead of having to list it multiple times. It will also get rid of the first subquery.

Answer 2

With this schema:
CREATE TABLE product
(
product_id int IDENTITY
, name varchar(50)
)
CREATE TABLE requirement
(
requirement_id int IDENTITY
, product_id int
, quantity int
, reward_id int
)
CREATE TABLE reward
(
reward_id int IDENTITY
, reward varchar(50)
)
CREATE TABLE purchased
(
purchased_id int IDENTITY
, product_id int
, quantity int
)
Your query becomes:
SELECT requirement.reward_id
FROM requirement
LEFT JOIN purchased
ON purchased.product_id = requirement.product_id
AND purchased.quantity >= requirement.quantity
GROUP BY requirement.reward_id
HAVING COUNT(purchased.product_id) = COUNT(requirement.reward_id);
Here's a SQLFiddle to play around with: http://sqlfiddle.com/#!3/e93c9/7