MySql Select - row subtract previous row

I'm trying to extract stats from DB. Table's structure is:

UpdatedId product_name   revenue
980       Product1       1000
975       Product1       950
973       Product1       900
970       Product1       800
965       Product21      1200

So revenue = previous revenue + new revenue.

In order to make graphs, the goal is to get the output for Product1 like this

UpdateId  Difference
980       50 
975       50 
973       100 
970       0 

I tried this query but MySQL gets stuck :)

select a.product_name, a.revenue, b.revenue, b.revenue- a.revenue as difference from updated_stats a, updated_stats b where a.product_name=b.product_name and b.revenue= (select min(revenue) from updated_stats where product_name=a.product_name and revenue > a.revenue and product_name= 'Product1')

Could you please tell me, how it should be queried? Thanks.

I would do this with a correlated subquery:

select u.*,
       (select u.revenue - u2.revenue
        from updated_stats u2
        where u2.product_name = u.product_name and
              u2.updatedid < u.updatedid
        order by u2.updatedid desc
        limit 1
       ) as diff
from updated_stats u;

Note: This returns NULL instead of 0 for 970. That actually makes more sense to me. But you can use COALESCE() or a similar function to turn it into a 0.

If updated_stats is even moderately sized, you will want an index on updated_status(product_name, updated_id, revenue). This index covers the subquery.