Comparing Value Ranges Between 2 Tables - sql

Question

I have an oracle 10g database that has 2 tables: a REBATES table, and an ORDERS table.
The REBATES table looks sort of like this:
| rebate_percentage | min_purchase |
------------------------------------
| 1.0 | 5000 |
| 1.5 | 7000 |
| 2.0 | 11000 |
| 5.0 | 20000 |
I'm trying to determine the rebate percentage to apply, based on total orders. I know how to find the sum of all orders for a particular customer, for a particular time range, but how do I also grab the rebate percentage, all in one query?
For example, if the order total is 16,000 then how can I construct a query that takes this value, compares it against the REBATES table, and returns 2.0?

Answer 1

In my opinion, the easiest way is if you have a min and max purchase amounts:
select rebate_percentage, min_purchase,
(lead(min_purchase, 1) over (order by min_purchase) - 1) as max_purchase
from rebates
Then you can do a simple between join, where the join condition looks like:
on totalorders between rebates.min_purchase and rebates.max_purchase
You can handle the final case (with NULLs) with a modified join condition:
on totalorders >= rebates.min_purchase and
(totalorders <= rebates.max_purchase or rebates.max_purchase is null)
Or, alternatively, by changing the original logic to have a coalesce() on the lead function with some very large value.

Answer 2

use Functions:
Example:
FUNCTION RebatePercentage(purchase Number) RETURN NUMBER IS
rebateVal NUMBER;
minPurchase NUMBER;
BEGIN
SELECT MAX(min_purchase)
INTO minPurchase
FROM REBATES
WHERE min_purchase <= purchase;
SELECT rebate_percentage
INTO rebateVal
FROM REBATES WHERE min_purchase = minPurchase;
RETURN ( rebateVal );
END;
Now you can call this function in your query
SELECT RebatePercentage(purchase_amt) from orders;