SQL Server set based processing for orders and details - sql-server

Question

I have been trying to get acclimated to set based processing with SQL Server. Below is a simplified version of cursor processing for this task. It involves creating an order from items in a shopping cart. The order is created, line items are added to the order details table, the total is accumulated and eventually updated on the order table. Can anyone suggest how to do this with a set based approach instead of a cursor?
One other question is that in most cases the cursor will process at most 10 or 12 line items at a time. Is that enough of a reason to not have to consider the set based approach?
declare getCart2 cursor for
select MemberID,ProductID,Quantity,Price
from Carts
where MemberID = #MemberID
open getCart2
fetch next from getCart2 into #MemberID,#ProductID,#Quantity,#Price
Insert into Orders
(MemberID,TotalAmount0
Values
(#MemberID, 0.00)
set #OrderID = ##Identity
while ##FETCH_STATUS = 0 Begin
Insert into OrderDetails
(OrderID,ProductID,Quantity)
Values
(#OderID,#ProductID,#Quantity)
set #TotalAmout = #TotalAmount + (#Quantity * #Price)
set #PrevMemberID = #MemberID
fetch next from getCart2 into #MemberID,#ProductID,#Quantity,#Price
End
close getCart2
deallocate getCart2
Update Orders
Set TotalAmount = #TotalAmount
Where OrderID = #OrderID
Thanks for your help.

Answer 1

Here goes an approach:
In this case I am creating a temporary table variable that will store the order id's on it.
Then, it performs the insertions on the Order table and after that, in the OrderDetails.
Finally, it computes the TotalAmount and updates on the Orders table.
Although you don't have it in your code (and in mine as well), but I recommend you to use this code inside a transaction.
Hope it helps you improve your performance.
USE [tempdb];
GO
SET NOCOUNT ON;
IF OBJECT_ID(N'dbo.Carts', N'U') IS NOT NULL DROP TABLE [dbo].[Carts];
IF OBJECT_ID(N'dbo.Orders', N'U') IS NOT NULL DROP TABLE [dbo].[Orders];
IF OBJECT_ID(N'dbo.OrderDetails', N'U') IS NOT NULL DROP TABLE [dbo].[OrderDetails];
GO
-- Creates the tables like you have
CREATE TABLE [dbo].[Carts] (MemberID INT, ProductID INT, Quantity INT, Price DECIMAL(10, 2));
CREATE TABLE [dbo].[Orders] (OrderID INT IDENTITY(1, 1), MemberID INT, TotalAmount DECIMAL(10, 2));
CREATE TABLE [dbo].[OrderDetails] (OrderID INT, ProductID INT, Quantity INT);
-- Inserts dummy data
INSERT INTO [dbo].[Carts] VALUES (1001, 80, 5, 25.00);
INSERT INTO [dbo].[Carts] VALUES (1002, 120, 2, 12.90);
INSERT INTO [dbo].[Carts] VALUES (1010, 70, 3, 12.00)
INSERT INTO [dbo].[Carts] VALUES (1034, 176, 5, 45.00);
-- Temporary table that stores the inserted Order ID's
DECLARE #OrdersToProcess TABLE (OrderID INT, MemberID INT);
-- Inserts all Orders
INSERT INTO Orders (MemberID, TotalAmount)
OUTPUT inserted.OrderID, inserted.MemberID INTO #OrdersToProcess
SELECT MemberID, 0
FROM [dbo].[Carts]
-- Inserts order details
INSERT INTO OrderDetails (OrderID, ProductID, Quantity)
SELECT OrderID, ProductID, Quantity
FROM [dbo].[Carts] C
INNER JOIN #OrdersToProcess O ON C.MemberID = O.MemberID;
-- Updates order totals
UPDATE [dbo].[Orders]
SET TotalAmount = T.Total FROM
(
SELECT OrderID, SUM(Quantity * Price) AS [Total]
FROM [dbo].[Carts] C
INNER JOIN #OrdersToProcess O ON C.MemberID = O.MemberID
GROUP BY OrderID
) T
WHERE [dbo].[Orders].OrderID = T.OrderID
SELECT * FROM [dbo].[Orders];
SELECT * FROM [dbo].[OrderDetails];
Results:

Answer 2

As I understand your problem, this store procedure should be called when a particular member presses the check-out button, so it should create a single order with all the items in the cart of that member.
You can use something like this:
INSERT INTO Orders (MemberID, TotalAmount)
VALUES (#MemberID, 0)
SET #OrderID=SCOPE_IDENTITY()
INSERT INTO OrderDetails (OrderID, ProductID, Quantity)
SELECT OrderID, ProductID, Quantity
FROM [dbo].[Carts] C
WHERE C.MemberID=#MemberID
UPDATE dbo.Orders SET TotalAmount=(
SELECT SUM(c.Quantity*c.Price)
FROM dbo.Carts c
WHERE c.MemberID=#MemberID
) WHERE OrderID=#OrderID
It's true that this reads the Carts table twice, but with a proper index (on the MemberID column) that should be fast enough.