Question

I want to implement SO like tags on userpost. I have a table called tag_data with columns tagId, title, count. I have a separate table that links the relationship between a post and the many tags it may use.

Heres the problem, how do i get the current count, increase or decrease it by one and store it SAFELY. So no other connection/thread will update it between the time i do select and update?

Answer 1

I assume you also want the new count, other wise this is a no brainer, just update set count=count+1.

If your db support output clause on UPDATE (eg. SQL Server 2K5 or 2K8):

UPDATE table
   SET count = count + 1
   OUTPUT inserted.count
   WHERE id=@id;

otherwise:

begin transaction
update table 
    set counter=counter+1
    where id=@id;
select counter
    from table
    where id=@id;
commit;