Query not bringing associated values with max function (Northwinds Database) - mysql

Question

I'm trying to get the product that has the highest gross value per category. I get the correct 'Grossed' amount by category, but it doesn't seem to bring the correct 'ProductID' and 'ProductName' with it.
SELECT
c.CategoryName,
prodGross.ProductID,
prodGross.ProductName,
MAX(ROUND(Grossed, 2)) AS Grossed
FROM
categories AS c
JOIN
(SELECT
p.ProductID,
p.ProductName,
p.CategoryID,
SUM(((od.UnitPrice * od.Quantity) - ((od.UnitPrice * od.Quantity) * od.Discount))) AS Grossed
FROM
northwind.`order details` AS od
JOIN products AS p ON p.ProductID = od.ProductID
GROUP BY p.ProductID) AS prodGross ON prodGross.CategoryID = c.CategoryID
GROUP BY c.CategoryName;
Any feedback would be helpful.
Thank you!

Answer 1

Consider derived tables of both aggregate queries matching the CategoryID and Grossed fields:
SELECT p.*, c.CategoryName, ROUND(g.MaxGrossed) AS HighestGrossed
FROM category c
INNER JOIN
(SELECT subp.ProductID, subp.ProductName, subp.CategoryID,
SUM(((od.UnitPrice * od.Quantity) -
((od.UnitPrice * od.Quantity) * od.Discount))) AS Grossed
FROM northwind.`order details` AS od
INNER JOIN products AS subp ON subp.ProductID = od.ProductID
GROUP BY subp.ProductID) As p
ON c.CategoryID = p.CategoryID
INNER JOIN
(SELECT subg.CategoryID, MAX(subg.Grossed) AS MaxGrossed
FROM
(SELECT subp.ProductID, subp.ProductName, subp.CategoryID,
SUM(((od.UnitPrice * od.Quantity) -
((od.UnitPrice * od.Quantity) * od.Discount))) AS Grossed
FROM northwind.`order details` AS od
INNER JOIN products AS subp ON subp.ProductID = od.ProductID
GROUP BY subp.ProductID) AS subg
GROUP BY subg.CategoryID) AS g
ON p.CategoryID = g.CategoryID AND p.Grossed = g.MaxGrossed
You can even save the repeated aggregate that calculates Grossed as a separate stored view and reference it in this query:
SELECT p.*, c.CategoryName, ROUND(g.MaxGrossed) AS HighestGrossed
FROM category c
INNER JOIN ProdGrossedView As p
ON c.CategoryID = p.CategoryID
INNER JOIN
(SELECT v.CategoryID, MAX(v.Grossed) AS MaxGrossed
FROM ProdGrossedView v
GROUP BY v.CategoryID) AS g
ON p.CategoryID = g.CategoryID AND p.Grossed = g.MaxGrossed