Could not get the expected query with SQL Server - sql

Question

I´m trying to do a SQL query but I couldn´t get the expected result. I really don´t know what is going wrong.
I have a table Product which contains (product_id, title) and other table Product_Variation which contains (product_variation_id, product_id, description, gender, price)
Basically, I have a product. For each product, have N variations.
e.g
Product: title "I have no idea"
Product_Variation: description "T-Shirt", gender "Male", price "59.90"
What I need is select Product and Product_Variation showing only the product with the lowest price.
I don´t care if a product has t-shirt, jacket or anything else as variation. I just need to get the variation which has the lowest price.
My query is:
SELECT b.product_id, b.title, MIN(b.price) as price, b.gender
FROM (
SELECT p.product_id, p.title, MIN(pv.price) AS price, pv.gender
FROM products p
join product_variation pv ON pv.product_id = p.product_id
GROUP BY p.product_id, p.title, pv.price, pv.gender
) b
GROUP BY b.product_id, b.title, b.price, b.gender
Pls, see my example in SQL Fiddle
Thanks!

Answer 1

Since you're using SQL 2008 you can use ROW_NUMBER to find the row with the lowest price:
SELECT *
FROM products p
INNER JOIN
(SELECT
product_id,
Description,
Gender,
Price,
ROW_NUMBER() OVER(PARTITION BY product_id ORDER BY price) Row
FROM product_variation )
pv ON pv.product_id = p.product_id
AND Row = 1
If you have two variations with the same price you'll get one random row.

Answer 2

-- Solution #1
SELECT *
FROM
(
SELECT p.product_id, p.title,
pv.price, pv.gender,
ROW_NUMBER() OVER(PARTITION BY p.product_id ORDER BY pv.price) AS row_num
FROM products p
join product_variation pv ON pv.product_id = p.product_id
) src
WHERE src.row_num = 1
-- Solution #2
SELECT p.product_id, p.title,
x.price, x.gender
FROM products p
cross apply
(
SELECT TOP(1) pv.price, pv.gender
FROM product_variation pv
WHERE pv.product_id = p.product_id
ORDER BY pv.price
) x

Answer 3

You can use the rank() window function to order stuff within a partition (group), but giving equal items the same rank:
;With b as (
Select
p.product_id,
p.title,
pv.price,
pv.gender,
rank() over(partition by p.product_id order by pv.price) rk
From
products p
Inner Join
product_variation pv
On pv.product_id = p.product_id
)
Select
b.product_id,
b.title,
b.price,
b.gender
From
b
Where
rk = 1
If you only want one per product even if there are equal products, use row_number() instead of rank()
Example Fiddle