Question

I am trying to achieve something like the following sql statements in a transaction. Can anyone advice how I can accomplish this? most importantly, there shouldnt be any dirty read or write. Thanks!

UPDATE items SET assigned = 1 
WHERE 
    SELECT TOP 1 @item_no = item_no
    FROM items
    WHERE item_code = @item_code 
    AND store_id = @store_id

UPDATE parts SET issued = 1 
WHERE 
    SELECT TOP 1 @part_no = part_no 
    FROM parts
    WHERE part_id = part_id 

INSERT INTO issued_hardware (@item_no, @part_no, DateTime.now, @username);

Answer 1

As other have mentioned you use a transaction and its isolation state to control Dirty Reads. I recommend against this since it means you can read an uncommitted transaction that may fail which can cause race conditions that are difficult to trace down.

Also since you’re doing more that one data modification you should probably explicitly roll back your transaction. Finally your SQL needed to fixed. Taking advantage of the output clause is probably a good idea.

BEGIN TRANSACTION;

BEGIN TRY


     DECLARE @Item table (item_no int )
     DECLARE @part table (part_no int)

     UPDATE TOP 1 ITEMS 
     SET assigned = 1
     WHERE   
            item_code = @item_code 
            AND store_id = @store_id
     OUTPUT
            inserted.item_no 
     INTO @Item 

     UPDATE TOP 1 parts 
     SET issued = 1
     OUTPUT
            inserted.part_no
     INTO @part


     INSERT INTO issued_hardware 
     SELECT item_no, GetDate(), @UserName
     FROM @item, @part;





END TRY
BEGIN CATCH
    IF @@TRANCOUNT > 0
        ROLLBACK TRANSACTION;
END CATCH;

IF @@TRANCOUNT > 0
    COMMIT TRANSACTION;
GO