Get sum of min values in each group from Mysql - php

Question

I am trying to retrieve the minimum price of some models.
Each model belongs to a certain group which belongs to a product.
I have the following tables:
Product
model_id product_id price
1 1 100
2 1 120
3 1 100
4 1 200
5 1 250
10 1 20
11 1 50
12 1 50
Product Overview
model_id product_id group_id
1 1 A
2 1 A
3 1 A
4 1 A
5 1 A
10 1 B
11 1 B
12 1 B
Product Group Optional
group_id product_id
B 1
Some groups could be optional, which means price will be zero unless the member wants to choose otherwise.
So in the example above, I want to get the sum of minimum price from each group.
We have two groups, group A and group B.
Group A minimum price value is 100 (model_id 1 and 3)
Group B minimum price value is 20 (model_id 10) but because Group B is optional then that means minimum price value is 0.
Overall sum of min values: 100 (Group A) + 0 (Group B) = 100
My code so far:
SELECT po.group_id,
CASE WHEN
((SELECT COUNT(*) FROM product_group_optional pgo
WHERE po.group_id = group_id AND po.product_id = 1 AND po.product_id = product_id) >= 1)
THEN SUM(0)
ELSE SUM(p.price)
END AS sum_price
FROM product_overview po, product p
WHERE po.product_id = 1
AND po.model_id = p.model_id
AND p.price = (
SELECT MIN(p2.price)
FROM product p2, product_overview po2
WHERE po2.product_id = 1 AND po2.group_id = po.group_id
AND po2.model_id = p2.model_id
)
GROUP BY po.group_id
The output:
group_id sum_price
A 200
B 0
The problem is that I get 200 for Group A but it should be 100.
There are 2 models with min value 100, model 1 and 3. And I assume these are sum together = 100 + 100 = 200.
Issue a) But I want to just take the min value, no matter how many times this value exists.
Issue b) Also, I am trying to get the SUM of those two output SUM of Group A and Group B.
But I am not sure how to do it.
I want it to be done in this query.
Desired output
Sum of all groups
100
Can anyone lead me to the right direction please?

Answer 1

You can use the following query:
SELECT SUM(min_price)
FROM (
SELECT po.group_id,
MIN(CASE WHEN pgo.group_id IS NULL THEN price ELSE 0 END) AS min_price
FROM Product AS p
INNER JOIN Product_overview AS po
ON p.product_id = po.product_id AND p.model_id = po.model_id
LEFT JOIN Product_group_optional AS pgo ON po.group_id = pgo.group_id
GROUP BY po.group_id) AS t

Answer 2

I'm not sure that I understand the keys of your tables, and the problem as well.
There is few questions.
a) The answer should be 120?
b) If the Product has no price, the is price null?
c) If there is a Product in a group with null price and others with price, should it be counted as 0?
Here is how you could get the sum of the lower prices of each group, ignoring the product_group_optional for while:
SELECT t2.group_id, sum(t2.new_price)
FROM
(
SELECT t.group_id, t.new_price
FROM
(
SELECT po.group_id, if(ifnull(pgo.product_id, true), p.price, 0) as new_price
FROM product p, product_overview po
LEFT JOIN product_group_optional pgo ON po.group_id = pgo.group_id
WHERE p.model_id = po.model_id
ORDER by po.group_id, new_price
) t
GROUP BY t.group_id
) t2