Inner join multiple SQL table and do calculations - sql

Question

I need to calculate in September 1996 what proportion of each product contribute to total revenue. The data are in 3 tables
Table #1: OrderDetails
OrderDetailID OrderID ProductID Quantity-
-------------------------------------------
1 10248 11 12
2 10248 42 10
3 10248 72 5
4 10249 14 9
5 10249 51 40
6 10250 41 10
Table #2: Products
ProductID ProductName SupplierID CategoryID Unit Price
-----------------------------------------------------------------------------------------------------
1 Chais 1 1 10 boxes x 20 bags 18
2 Chang 1 1 24 - 12 oz bottles 19
3 Aniseed Syrup 1 2 12 - 550 ml bottles 10
4 Chef Anton's Cajun Seasoning 2 2 48 - 6 oz jars 22
5 Chef Anton's Gumbo Mix 2 2 36 boxes 21.35
6 Grandma's Boysenberry Spread 3 2 12 - 8 oz jars 25
7 Uncle Bob's Organic Dried Pears 3 7 12 - 1 lb pkgs. 30
Table #3: Orders
OrderID CustomerID EmployeeID OrderDate ShipperID
------------------------------------------------------
10248 90 5 1996-07-04 3
10249 81 6 1996-07-05 1
10250 34 4 1996-07-08 2
10251 84 3 1996-07-08 1
10252 76 4 1996-07-09 2
10253 34 3 1996-07-10 2
10254 14 5 1996-07-11 2
I guess the steps are:
inner join OrderDetails with Order by OrderID to only show Orders in Sep 1996
inner join the result in step 1 with Products by ProductID and calculate each product's revenue percentage over total revenue
I've done step one
SELECT
Orders.OrderID,
Orders.OrderDate,
OrderDetails.Quantity,
OrderDetails.ProductID
FROM
Orders
INNER JOIN
OrderDetails ON Orders.OrderID = OrderDetails.OrderID
WHERE
OrderDate LIKE '1996-09%';
The expected result:
OrderID OrderDate Quantity ProductID
-----------------------------------------
10295 1996-09-02 4 56
10296 1996-09-03 12 11
10296 1996-09-03 30 16
10296 1996-09-03 15 69
10297 1996-09-04 60 39
But I don't know how to do step 2. Any suggestions please ? thank you very much!

Answer 1

Use window functions:
SELECT od.ProductID,
SUM(od.Quantity),
SUM(od.Quantity) * 1.0 / SUM(SUM(od.Quantity)) OVER () as ratio
FROM Orders o INNER JOIN
OrderDetails od
ON o.OrderID = od.OrderID
WHERE o.OrderDate >= '1996-09-01' AND o.OrderDate < '1996-10-01'
GROUP BY od.ProductID;

Answer 2

It looks like W3Cschool's interactive SQL practice doesn’t support window functions. Moreover, I didn’t find a way to define a variable, so had to mention the same constant (year and month) twice. In real life I would suggest using of analytic functions or at least declare a variable for a value used in several places.
Anyway, it looks like the following code doing what you need:
SELECT
od.ProductID,
MIN(o.OrderDate) as SalesStart,
MAX(o.OrderDate) as SalesEnd,
SUM(od.Quantity) as SoldQty,
SUM(od.Quantity * p.Price) as SoldAmt,
SUM(od.Quantity * p.Price) * 1.0 /
(
SELECT SUM(odAll.Quantity * pAll.Price)
FROM OrderDetails odAll
INNER JOIN Orders as oAll
ON oAll.OrderID = odAll.OrderID
INNER JOIN Products as pAll
ON odAll.ProductID = pAll.ProductID
WHERE oAll.OrderDate LIKE '1996-09%') as PortionInTotalSales
FROM Orders as o
INNER JOIN OrderDetails as od
ON o.OrderID = od.OrderID
INNER JOIN Products as p
ON od.ProductID = p.ProductID
WHERE o.OrderDate LIKE '1996-09%'
GROUP BY od.ProductID