Question

Basically I am doing a movie rental company database.
I need to be able to Give the names of movies that made more money than any other movie within their category.

Currently, I have a product table and rental table.

Product – 
Attributes: (Product_ID, Product_Title, Rating, Release_Date, Genre, Length_of_Movie, Director_Name, Key_Actor, Num_Copies)
PK – Product_ID

Rental – 
Attributes: (Rental_ID, Member_ID, Product_ID, Date_Rented, Date_Returned)
PK – Rental_ID
FK – Member_ID, Product ID

Each rental has a value of $1.00. I was able able to get the revenue of all the rentals, but I am struggling to get it by genre or category. I got the revenue as a whole by this query:

Select sum(count(Rental_ID) *1) as Revenue 
from Rental
Group by Rental_ID;       

** every rental is $1.00 so it was a simple calculation to just count how many times a unique rental number was created and multiply it by the flat fee.

I now need to break that down, and give the highest earner per genre or category. I’m completely stumped… any help would be appreciated. Thanks.

Answer 1

I haven’t test this but:

I’d create a view to get revenue per product like so

Create View RevenuePerProduct As
Select
  r.Product_ID,
  Count(*) As Revenue -- as $1/rental we can just count
From
  Rental r
Group By
  r.Product_ID

To get the maximum earnings by Genre you can utilise the view, and I’ll make another view called MaxRevenueByGenre.

Create View MaxRevenueByGenre As
Select
  p.Genre,
  Max(rpp.Revenue) As MaxByGenre
From 
  RevenuePerProduct rpp
    Inner Join
  Product p
    On rpp.Product_ID = p.Product_ID
Group By
  p.Genre

To get the product (or products) that had the maximum revenue per genre is a bit more tricky as you need to refer to the revenue part twice. You’ll notice both views are used.

Select
  best.Genre,
  best.ProductTitle,
  rpp.Revenue
From
  Product best
    Inner Join
  RevenuePerProduct rpp
    On best.Product_ID = rpp.Product_ID
    Inner Join 
  MaxRevenueByGenre mpg
    On best.Genre = mpg.Genre And rpp.Revenue = mpg.MaxByGenre

This will produce more than one result for each Genre if they are tied for highest earner.

You can get by without views, by substituting the select statements of the view inside parenthesis if you prefer.