Apply a discount to order if user already ordered something else - sql

Question

I have a table with users, a table with levels, a table for submitted orders and processed orders.
Here's what the submitted orders looks like:
OrderId UserId Level_Name Discounted_Price Order_Date Price
1 1 OLE Core 0 2020-11-01 00:00:00.000 19.99
2 1 Xandadu 1 2020-11-01 00:00:00.000 0
3 2 Xandadu 0 2020-12-05 00:00:00.000 5
4 1 Eldorado 1 2021-01-31 00:00:00.000 9
5 2 Eldorado 0 2021-02-20 00:00:00.000 10
6 2 Birmingham Blues NULL 2021-07-10 00:00:00.000 NULL
What I am trying to do:
UserId 2 has an order for Birmingham Blues, they have already ordered Eldorado and so qualify for a discount on their Birmingham Blues order. Is there a way to check the entire table for this similarity, and if it exists update the discounted price to a 1 and change the price to lets say 10 for the Birmingham Blues order.
EDIT: I have researched the use of cursors, which I'm sure will do the job but they seem complicated and was hoping a simpler solution would be possible. A lot of threads seem to also avoid using cursors. I also looked at this question: T-SQL: Deleting all duplicate rows but keeping one and was thinking I could potentially use the answer to that in some way.

Answer 1

Based on your description and further comments, the following should hopefully meet your requirements - updating the row for the specified User where the values are currently NULL and the user has a qualifying existing order:
update s set
s.Discounted_Price = 1,
Price = 10
from submitted_Orders s
where s.userId=2
and s.Level_Name = 'Birmingham Blues'
and s.discounted_Price is null
and s.Price is null
and exists (
select * from submitted_orders so
where so.userId = s.userId
and so.Level_name = 'Eldorado'
and so.Order_Date < s.OrderDate
);