Sum of all values except the first - sql

Question

I have the following three tables:
Customers:
Cust_ID,
Cust_Name
Products:
Prod_ID,
Prod_Price
Orders:
Order_ID,
Cust_ID,
Prod_ID,
Quantity,
Order_Date
How do I display each costumer and how much they spent excluding their very first purchase?
[A] - I can get the total by multiplying Products.Prod_Price and Orders.Quantity, then GROUP by Cust_ID
[B] - I also can get the first purchase by using TOP 1 on Order_Date for each customer.
But I couldnt figure out how to produce [A]-[B] in one query.
Any help will be greatly appreciated.

Answer 1

For SQL-Server 2005, 2008 and 2008R2:
; WITH cte AS
( SELECT
c.Cust_ID, c.Cust_Name,
Amount = o.Quantity * p.Prod_Price,
Rn = ROW_NUMBER() OVER (PARTITION BY c.Cust_ID
ORDER BY o.Order_Date)
FROM
Customers AS c
JOIN
Orders AS o ON o.Cust_ID = c.Cust_ID
JOIN
Products AS p ON p.Prod_ID = o.Prod_ID
)
SELECT
Cust_ID, Cust_Name,
AmountSpent = SUM(Amount)
FROM
cte
WHERE
Rn >= 2
GROUP BY
Cust_ID, Cust_Name ;
For SQL-Server 2012, using the FIRST_VALUE() analytic function:
SELECT DISTINCT
c.Cust_ID, c.Cust_Name,
AmountSpent = SUM(o.Quantity * p.Prod_Price)
OVER (PARTITION BY c.Cust_ID)
- FIRST_VALUE(o.Quantity * p.Prod_Price)
OVER (PARTITION BY c.Cust_ID
ORDER BY o.Order_Date)
FROM
Customers AS c
JOIN
Orders AS o ON o.Cust_ID = c.Cust_ID
JOIN
Products AS p ON p.Prod_ID = o.Prod_ID ;
Another way (that works in 2012 only) using OFFSET FETCH and CROSS APPLY:
SELECT
c.Cust_ID, c.Cust_Name,
AmountSpent = SUM(x.Quantity * x.Prod_Price)
FROM
Customers AS c
CROSS APPLY
( SELECT
o.Quantity, p.Prod_Price
FROM
Orders AS o
JOIN
Products AS p ON p.Prod_ID = o.Prod_ID
WHERE
o.Cust_ID = c.Cust_ID
ORDER BY
o.Order_Date
OFFSET
1 ROW
-- FETCH NEXT -- not needed,
-- 20000000000 ROWS ONLY -- can be removed
) AS x
GROUP BY
c.Cust_ID, c.Cust_Name ;
Tested at SQL-Fiddle
Note that the second solution returns also the customers with only one order (with the Amount as 0) while the other two solutions do not return those customers.

Answer 2

Which version of SQL? If 2012 you might be able to do something interesting with OFFSET 1, but I'd have to ponder much more how that works with grouping.
EDIT: Adding a 2012 specific solution inspired by #ypercube
I wanted to be able to use OFFSET 1 within the WINDOW to it al in one step, but the syntax I want isn't valid:
SUM(o.Quantity * p.Prod_Price) OVER (PARTITION BY c.Cust_ID
ORDER BY o.Order_Date
OFFSET 1)
Instead I can specify the row boxing, but have to filter the result set to the correct set. The query plan is different from #ypercube's, but the both show 50% when run together. They each run twice as as fast as my original answer below.
WITH cte AS (
SELECT c.Cust_ID
,c.Cust_Name
,SUM(o.Quantity * p.Prod_Price) OVER(PARTITION BY c.Cust_ID
ORDER BY o.Order_ID
ROWS BETWEEN 1 FOLLOWING
AND UNBOUNDED FOLLOWING) AmountSpent
,rn = ROW_NUMBER() OVER(PARTITION BY c.Cust_ID ORDER BY o.Order_ID)
FROM Customers AS c
INNER JOIN
Orders AS o ON o.Cust_ID = c.Cust_ID
INNER JOIN
Products AS p ON p.Prod_ID = o.Prod_ID
)
SELECT Cust_ID
,Cust_Name
,ISNULL(AmountSpent ,0) AmountSpent
FROM cte WHERE rn=1
My more general solution is similar to peter.petrov's, but his didn't work "out of the box" on my sample data. That might be an issue with my sample data or not. Differences include use of CTE and a NOT EXISTS with a correlated subquery.
CREATE TABLE Customers (Cust_ID INT, Cust_Name VARCHAR(10))
CREATE TABLE Products (Prod_ID INT, Prod_Price MONEY)
CREATE TABLE Orders (Order_ID INT, Cust_ID INT, Prod_ID INT, Quantity INT, Order_Date DATE)
INSERT INTO Customers SELECT 1 ,'Able'
UNION SELECT 2, 'Bob'
UNION SELECT 3, 'Charlie'
INSERT INTO Products SELECT 1, 10.0
INSERT INTO Orders SELECT 1, 1, 1, 1, GetDate()
UNION SELECT 2, 1, 1, 1, GetDate()
UNION SELECT 3, 1, 1, 1, GetDate()
UNION SELECT 4, 2, 1, 1, GetDate()
UNION SELECT 5, 2, 1, 1, GetDate()
UNION SELECT 6, 3, 1, 1, GetDate()
;WITH CustomersFirstOrder AS (
SELECT Cust_ID
,MIN(Order_ID) Order_ID
FROM Orders
GROUP BY Cust_ID
)
SELECT c.Cust_ID
,c.Cust_Name
,ISNULL(SUM(Quantity * Prod_Price),0) CustomerOrderTotalAfterInitialPurchase
FROM Customers c
LEFT JOIN (
SELECT Cust_ID
,Quantity
,Prod_Price
FROM Orders o
INNER JOIN
Products p ON o.Prod_ID = p.Prod_ID
WHERE NOT EXISTS (SELECT 1 FROM CustomersFirstOrder a WHERE a.Order_ID=o.Order_ID)
) b ON c.Cust_ID = b.Cust_ID
GROUP BY c.Cust_ID
,c.Cust_Name
DROP TABLE Customers
DROP TABLE Products
DROP TABLE Orders

Answer 3

Try this. It should do it.
SELECT c1.cust_name ,
c1.cust_id ,
SUM(p1.Prod_Price)
FROM orders o1
JOIN products p1 ON o1.prod_id = p1.prod_id
JOIN customers c1 ON o1.cust_id = c1.cust_id
LEFT JOIN ( SELECT o2.cust_id ,
MIN(o2.Order_Date) AS Order_Date
FROM orders o2
GROUP BY o2.cust_id
) t ON o1.cust_id = t.cust_id
AND o1.Order_Date = t.Order_Date
WHERE t.Order_Date IS NULL
GROUP BY c1.cust_name ,
c1.cust_id

Answer 4

You have to number orders by Customer and then you can have the amount for the first order and next orders with a CTE and ROW_NUMBER() like this:
; WITH NumberedOrders
AS ( SELECT Customers.Cust_Id ,
Customers.Cust_Name ,
ROW_NUMBER() OVER ( ORDER BY Customers.Cust_id ) AS Order_Number ,
Orders.Order_Date ,
Products.Prod_price * Orders.Quantity AS Amount
FROM Orders
INNER JOIN Customers ON Orders.Cust_Id = Customers.Cust_Id
INNER JOIN Products ON Orders.Prod_Id = Products.Prod_Id
)
SELECT Cust_Id ,
SUM(CASE WHEN Order_Number = 1 THEN Amount
ELSE 0
END) AS A_First_Order ,
SUM(CASE WHEN Order_Number = 1 THEN 0
ELSE Amount
END) AS B_Other_orders ,
SUM(Amount) AS C_All_orders
FROM NumberedOrders
GROUP BY Cust_Id
ORDER BY Cust_Id