Generating a unique batch id (SQL Server) - sql

Question

This is possible 2x questions in 1x. Sorry about that, but here goes:
PROBLEM
I am creating a unique batch id everytime a user uploads some data to SQL Server. Currently, I do this by looking at the last value of the 'Identity Specification' and add +1 to that.
Problem arises, as you might have guessed, if multiple users input data at the same, they both would get the same batch id...
Possible Solution
In order to mitigate this issue, I have come up with this method to generate 3 letter + random number; and the (last id value + 1):
DECLARE #tmp CHAR(3) = CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65);
SELECT #tmp;
select cast(RAND()*9999 as int)
(1) I am not sure how to concatenate this into one line of string.
(2) The other question, is there a way to 100% guarantee every user is given a unique batch id every time they submit a request, regardless of how many are doing it simultaneously?
I would really appreciate your input in this.

Answer 1

1 - Concatenation part is very simple, you can do the following:
DECLARE #tmp VARCHAR(10);
SET #tmp = CHAR(CAST(RAND()*26 AS int)+65)
+ CHAR(CAST(RAND()*26 AS int)+65)
+ CHAR(CAST(RAND()*26 AS int)+65)
+ CAST(cast(RAND()*9999 as int) AS VARCHAR(4));
SELECT #tmp;
2 - I would suggest to populate a table with the Random values you would like to issue to users and then select from it, to avoid the race-condition.
Create a table called BatchNumbers with two Columns BatchNumber and Used.
Populate the batch number table and 0 as default value for Used Column.
Then everytime you need a batch number do the following.
CREATE PROC dbo.usp_Get_BatchNumber
#BatchNumber VARCHAR(10) OUTPUT
AS
BEGIN
SET NOCOUNT ON;
Declare #t TABLE (BN VARCHAR(10));
UPDATE TOP (1) BatchNumbers
SET Used = 1
OUTPUT inserted.BatchNumber INTO #t (BN )
WHERE Used = 0;
SELECT #BatchNumber = BN FROM #t;
END

Answer 2

You need an "Upload" table with a Bigint Identity column for the BatchID, then add a new row for every user upload.
The server will maintain the correct values and prevent collisions.

Answer 3

I would use the built in function for this:
select newid()
> 240CA878-135E-4176-AE57-0FA83FF74037

Answer 4

For the first problem, you can either create a variable for your random number as a char(4) and just simply concatenate the 2, or create it as an int and then CAST it as a VARCHAR while concatenating. Everything that is concatenated into a string must be a string.
DECLARE #tmp CHAR(3) = CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65);
SELECT #tmp;
DECLARE #randNum VARCHAR(4) = CAST(RAND()*9999 AS INT)
-- OR DECLARE #randNum INT = CAST(Rand()*9999) AS INT)
SELECT #randNum
DECLARE #batchID VARCHAR(MAX) = #tmp + #randNum
-- OR DECLARE #batchID VARCHAR(MAX) = #tmp + CAST(#randNum AS VARCHAR)
SELECT #batchID

Answer 5

try the following:
1)
DECLARE #tmp CHAR(7) = CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65) + CHAR(CAST(RAND()*26 AS int)+65) + cast(cast(RAND()*9999 as int) as varchar(4));
SELECT #tmp;
2) Yes, I think so.

Answer 6

I upvoted Terry Carmen's answer, but from his comments it sounds like he's suggesting something different from what I first thought, so here's a complete example. I think you want a table that has a key defined with the IDENTITY property, which will tell SQL Server that you want unique, sequential values in that column and you want the database to worry about the details of guaranteeing that this is so.
create table dbo.Import
(
-- identity(1, 1) means that SQL Server will automatically assign values for
-- this column when you insert a record, with 1 being the first value
-- assigned and each subsequent value incrementing by 1.
Identifier bigint not null identity(1, 1),
-- This column for illustration only; replace it with whatever data you need
-- to store.
YourStuffHere varchar(max)
);
-- Now simply use any INSERT or MERGE command against dbo.Import, and omit the
-- Identifier column from the list of columns whose values the command supplies.
-- Then you can use the SCOPE_IDENTITY() function or an OUTPUT clause to capture
-- the Identifier value that SQL Server has inserted.
-- Example 1: INSERT with explicit values and OUTPUT.
insert dbo.Import
(YourStuffHere)
output
inserted.Identifier
values
('Example 1');
-- Example 2: INSERT/SELECT with OUTPUT.
insert dbo.Import
(YourStuffHere)
output
inserted.Identifier
select
'Example 2';
-- Example 3: INSERT with SCOPE_IDENTITY().
insert dbo.Import
(YourStuffHere)
values
('Example 3');
select Identifier = convert(bigint, scope_identity());
-- Show table contents.
select * from dbo.Import;
The first INSERT statement above produces the following result:
Identifier
1
The second:
Identifier
2
The SELECT following the third INPUT gives:
Identifier
3
And the final SELECT shows you the contents of the table:
Identifier YourStuffHere
1 Example 1
2 Example 2
3 Example 3
This is the easiest way to go about this as it allows SQL Server to do all the real work for you. Please let me know if I've misunderstood your requirements.