SQL Server Transaction inside stored procedure - sql

Question

Suppose, i have two tables Product and ProductSales.
Product table has:
ProductID(int)(pk)
Name(varchar2)
UnitPrice(float)
ProductAvailable(int)
ProductSales table has:
ProductSalesID(int)(pk)
ProductID(int)
Quantity(int)
I want to create a transaction inside stored procedure that first checks if the Quantity is less than ProductAvailable. If it is greater then Rollback the transaction else Deduct the Quantity(given by user) from ProductAvailable and also insert into ProductSales table.
how can i solve the scenario using SQL Server

Answer 1

Solution for concurrent updates:
-- Test Data
CREATE TABLE Product (
ProductID int NOT NULL IDENTITY PRIMARY KEY CLUSTERED
,Name varchar(256) NOT NULL
,UnitPrice money NOT NULL
,ProductAvailable int NOT NULL)
CREATE TABLE ProductSales (
ProductSalesID int NOT NULL IDENTITY PRIMARY KEY CLUSTERED
,ProductID int NOT NULL
,Quantity int NOT NULL)
INSERT INTO Product (Name, UnitPrice, ProductAvailable)
VALUES ('Prod1', 5.0, 10)
,('Prod2',6.0, 5)
GO
First variant - MSDN OUTPUT Clause
CREATE PROCEDURE Sale
#ProductID int
,#Quantity int
AS
BEGIN
IF #Quantity <= 0 RETURN -1;
-- atomic operation
UPDATE Product
SET ProductAvailable = ProductAvailable - #Quantity
OUTPUT INSERTED.ProductID, #Quantity INTO ProductSales (ProductID, Quantity)
WHERE ProductID = #ProductID
AND ProductAvailable >= #Quantity;
IF ##ROWCOUNT = 0 RETURN -1;
END
GO
But it has limitation - output_table cannot:
Have enabled triggers defined on it.
Participate on either side of a FOREIGN KEY constraint.
Have CHECK constraints or enabled rules.
Second variant - MSDN Transaction Statements
CREATE PROCEDURE Sale2
#ProductID int
,#Quantity int
AS
BEGIN
DECLARE #ProcID CHAR(36) = NEWID()
,#TranCount Int = ##TranCount
,#ProductAvailable int
,#errorMessage nvarchar(4000)
,#errorSeverity int
,#errorState int
,#ReturnCode int = -1;
IF #Quantity <= 0 RETURN -1;
IF (#TranCount = 0)
BEGIN TRANSACTION;
ELSE
SAVE TRANSACTION #ProcID;
BEGIN TRY
SELECT #ProductAvailable = ProductAvailable
FROM Product WITH (XLOCK, HOLDLOCK)
WHERE ProductID = #ProductID;
-- Record is locked, you can do any checks here
IF #ProductAvailable >= #Quantity
BEGIN
UPDATE Product
SET ProductAvailable = ProductAvailable - #Quantity
WHERE ProductID = #ProductID;
INSERT INTO ProductSales (ProductID, Quantity)
VALUES(#ProductID, #Quantity);
SET #ReturnCode = 1;
END
ELSE
SET #ReturnCode = -1;
IF (#TranCount = 0)
COMMIT TRANSACTION;
END TRY
BEGIN CATCH
IF (#TranCount = 0)
ROLLBACK TRANSACTION;
ELSE
IF (XACT_STATE() <> -1)
ROLLBACK TRANSACTION #ProcID;
SELECT #errorMessage = 'Error in [Sale2]: ' + ERROR_MESSAGE(), #errorSeverity = ERROR_SEVERITY(), #errorState = ERROR_STATE();
RAISERROR (#errorMessage, #errorSeverity, #errorState);
SET #ReturnCode = -1;
END CATCH
RETURN #ReturnCode;
END
GO
Check result
-- Test
DECLARE #RetCode int
EXEC #RetCode = Sale #ProductID = 1, #Quantity = 7
SELECT #RetCode as RetCode
EXEC #RetCode = Sale2 #ProductID = 1, #Quantity = 2
SELECT #RetCode as RetCode
EXEC #RetCode = Sale #ProductID = 2, #Quantity = 7
SELECT #RetCode as RetCode
GO
SELECT * FROM ProductSales
SELECT * FROM Product
GO