What you are looking for is called Optimistic Concurrency Control.
Add an int column to your table called version. Start at 0.
Read a row:
select whatever, version from mytable where id=1
Results:
something, 0
Update a row:
update mytable set whatever = something_new, version = 1 where id = 1 and version = 0
If that row was not found, raise an exception.
If you use an ORM like Hibernate, you can just add a field with a @Version annotation and it will handle this for you.