MySQL join next lower value from other table - mysql

Question

I've the two tables orders
id article amount
1 1 1
2 2 50
and prices
id article min_amount price
1 1 1 42.99
2 2 1 5.06
3 2 5 4.55
4 2 10 4.3
5 2 25 4.05
6 2 100 2.66
The prices tables contains IDs of articles and a minimum amount you would have to buy to get a bulk discount (which would change the price for the order). I would like to join prices into orders, so that the result looks like:
id article amount price
1 1 1 42.99
2 2 50 4.05
The order id 2 is above the minimum (25) to get the article for 4.05€, but still below 100 at which you would get a bigger discount, so the query would to have pick the next-lower value.
I've tried this query so far
SELECT
orders.id AS id,
orders.article,
orders.amount,
prices.price,
(orders.amount - prices.min_amount) AS discount_diff
FROM orders
LEFT JOIN prices ON (prices.article = orders.article) AND (prices.min_amount <= orders.amount)
which gives this result
id article amount price discount_diff
1 1 1 42.99 0
2 2 50 5.06 49
2 2 50 4.55 45
2 2 50 4.3 40
2 2 50 4.05 25
You can find this example on "js"fiddle: http://sqlfiddle.com/#!9/1b2bf/8

Answer 1

The query you need is this:
SELECT orders.id AS id,
orders.article,
orders.amount,
prices.price
FROM orders
INNER JOIN prices ON ( prices.article = orders.article
and prices.min_amount <= orders.amount)
INNER JOIN ( SELECT orders.article,
orders.amount,
min(prices.price) minprince
FROM orders
INNER JOIN prices ON (prices.article = orders.article
AND prices.min_amount <= orders.amount)
GROUP BY orders.article,
orders.amount) b
ON ( prices.article = b.article
AND orders.amount = b.amount
AND prices.price = b.minprince)
See it here: http://sqlfiddle.com/#!9/1b2bf/27