Find difference between two consecutive rows of same column in mysql

Question

I'm having a situation where I need to calculate the difference between two consecutive rows of same column. Here is my table named 'orders' structure.

orderid   type     productsales
1002      Order    120         
1002      Refund   -35   
1003      Order    199           
1003      Refund   -50            
1004      Order    245
1005      Order    80

Now, what I want to Select only those records where the 'productsales' difference between the same orderids of order type 'Order' & 'Refund' is greater than 0

Answer 1

select orderid
from orders
group by orderid
having sum(case when `type` = 'Order' then productsales else 0 end) +
       sum(case when `type` = 'Refund' then productsales else 0 end) > 0

You need to subtract the values from another. But since you stored the - in the refund I used + .