How to join or subquery a table representing tiers - mysql

Question

I have a fee table that contains fees in a list of price cutoffs based on item pricing. For example the first fee range is for items that are priced at $0 and up to the next tier have a $1 fee. Items that have a price of $25 up to the next tier have a $2 fee, etc. Here is the fee table:
Fee
Cutoff Fee
------ ---
0 1
25 2
100 3
Here is the item table with the prices:
Item
Id Price
------ ------
1 32
2 18
3 2
4 100
The result should look like this:
Desired Item Fees Result
Id Price Fee Total Price with fee
----- ------- ------- -----------
1 32 2 34
2 18 1 19
3 2 1 3
4 100 3 103
Creating the result has been challenging. Here is what the cartesian product of the join result looks like between the two tables:
Id Price Cutoff Fee
--- ------- ------- ---
1 32 0 1 -- eliminate because price is above the next cut 25
2 18 0 1
3 2 0 1
4 100 0 1 -- eliminate because price is above the next cut 25
1 32 25 2
2 18 25 2 -- eliminate because price is below this cut
3 2 25 2 -- eliminate because price is below this cut
4 100 25 2 -- eliminate because price is above (equal to) the next cut 100
1 32 100 3 -- eliminate because price is below this cut
2 18 100 3 -- eliminate because price is below this cut
3 2 100 3 -- eliminate because price is below this cut
4 100 100 3
the first where is simple:
where price >= cut
this narrows the list down to:
Id Price Cutoff Fee
--- ------- ------- ---
1 32 0 1 -- eliminate because price is above the next cut 25
2 18 0 1
3 2 0 1
4 100 0 1 -- eliminate because price is above the next cut 25
1 32 25 2
4 100 25 2 -- eliminate because price is above (equal to) the next cut 100
4 100 100 3
Here's the question: how do i filter out records that are in the next pricing tier? This is the sql i have so far.
select price, cutoff, fee from item, fee
where price >= cutoff;
I have tried a subquery:
select price, cutoff, fee,
(select min(cutoff), fee from fee where cutoff > price) as nextfee
from item, fee
where price >= cutoff;
but this gives the error:
Operand should contain 1 Column(s)

Answer 1

One way to approach this problem is to use a correlated subquery to get the first fee in the fee table where the cutoff is greater than or equal to the price:
select id, price, fee, (price + fee) as totalprice
from (select id, price,
(select fee
from fee
where price >= cutoff
order by cutoff desc
limit 1
) as fee
from item
) i

Answer 2

What about this? No subjoins, better for performance and simpler.
SELECT i.id, i.price, MAX(f.fee), i.price + MAX(f.fee)
FROM item i INNER JOIN fee f
ON i.price > f.cutoff
GROUP BY i.id, i.price