Question

I have 2 tables (A,B), and 1 query

My query is something like this

1. Read From A
2. Update B with this data from A
3. Using the updated table B, set final value of A.

Example execution can be find in below question:
Proper way to keep a single data in sql server?

Now since all the process is connected, this query should not be executed twice at the same time, or by 2 different users until the process ends. How do I prevent this ? Or does it already work securely like this?

Answer 1

Use transaction lock :

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
GO

BEGIN TRANSACTION

--select * from A
-- update B ....
--update A

WAITFOR DELAY '00:00:02'   -- tables remain locked for 2 secs   hh:mm:ss

commit TRANSACTION

during the transaction execution, any try to read or write from/to tables will timeout…