SQL stored procedure inserting duplicate OrderNumber - sql

Question

I searched the Internet for days, no effort, maybe I cant ask in a right way.
I have a sql table like this:
create table Items
(
Id int identity(1,1),
OrderNumber varchar(7),
ItemName varchar(255),
Count int
)
Then I have a stored procedure inserting items, on demand creating new OrderNumber:
create procedure spx_insertItems
#insertNewOrderNr bit,
#orderNumber varchar(7),
#itemName varchar(255),
#count int
as
begin
set nocount on;
if (#insertNewOrderNr = 1)
begin
declare #newNr = (select dbo.fun_getNewOrderNr())
INSERT INTO Items (OrderNumber, ItemName, Count) values (#newNr, #itemName, #count)
select #newNr
end
else
begin
INSERT INTO Items (OrderNumber, ItemName, Count) values (#orderNumber, #itemName, #count)
select scope_identity()
end
end
Finally there is a user defined function returning new OrderNumber:
create function dbo.fun_getNewOrderNr
()
return varchar(7)
as
begin
/* this func works well */
declare #output varchar(7)
declare #currentMaxNr varchar(7)
set #currentMaxNr = (isnull((select max(OrderNumber) from Items), 'some_default_value_here')
/* lets assume the #currentMaxNr is '01/2014', here comes logic that increments to #newValue='02/2014' and sets to #output, so: */
set #output = #newValue
return #output
end
Into Items can be inserted items that do as well that do not belong to any OrderNumber.
Whether an Item should become new OrderNumber, the procedure is called with #insertNewOrderNr=1, returns the new order number, that can be used to insert next items with that OrderNumber while #insertNewOrderNr=0.
Occasionally there happens that there come simultaneously 2 requests to #insertNewOrderNr and THERE IS THE PROBLEM - Items, that should correspond with different OrderNumbers get the same OrderNumber.
I tried to use transaction with no success.
The table structure cant be modified by me.
What would be the right way to ensure, that there won't be used the same newOrderNumber when simultaneous requests to the procedure come?
I am stuck here for a long time till now. Please, help.

Answer 1

You will have that problem as long as you use MAX(OrderNumber).
You might consider using sequences:
Create sequence
CREATE SEQUENCE dbo.OrderNumbers
AS int
START WITH 1
INCREMENT BY 1
NO CACHE;
GO
CREATE SEQUENCE dbo.OrderNumberYear
AS int
START WITH 2014
INCREMENT BY 1
NO CACHE;
SELECT NEXT VALUE FOR dbo.OrderNumberYear; --Important, run this ONE time after creation, this years value must be returned one initial time to work correctly.
Insert code
DECLARE #orderNumberYear INT = (SELECT CONVERT(INT, current_value) FROM sys.sequences WHERE name = 'OrderNumberYear');
IF(#orderNumberYear < YEAR(GETDATE()))
BEGIN
SELECT #orderNumberYear = NEXT VALUE FOR dbo.OrderNumberYear;
ALTER SEQUENCE dbo.OrderNumbers RESTART WITH 1 ;
END
IF(#orderNumberYear != YEAR(GETDATE()))
RAISERROR(N'Order year sequence is out of sync.', 16, 1);
DECLARE #newNr VARCHAR(15) = CONCAT(FORMAT(NEXT VALUE FOR dbo.OrderNumbers, '00/', 'en-US'), #orderNumberYear);
INSERT INTO Items (OrderNumber, ItemName, Count) values (#newNr, #itemName, #count)
SELECT #newNr

Answer 2

The duplicity still occured, not so often, but did.
The trick I finally used to get around didn't find itself inside SQL. Since the DB is always used by ONLY one web app that is used by several users, this is the solution:
in all (about 5) places in my VB.NET code I surrounded the myCommand.ExecuteScalar() with SyncLock (read more) statement that DID the trick :)