MS SQL : Use Computed value to Compute other values

Question

I'm having problem with generating results which are computed from data that exists in database. This is the case

I have Coupons that can be amount or percent, if percent is 0 then amount is used

CASE 
  WHEN c.CouponPercent > 0 THEN p.Price - (c.CouponPercent/100)
  ELSE c.CouponValue
END as Coupon

now I have to calculate percent for one content provider that is

(p.Price-Coupon)*(ProviderPercent/100)

How can I use calculate coupon value from above to calculate Provider percent, if I use it as in code above error is reported "Invalid column name 'Coupon'".

Please help me, i Know how to resolve this on difficult way which is calculate Coupon value each time when calculating ProviderPercent but I have 8 percents like this in one report for different providers.

So basically question is how to use computed Coupon value to use it in another calculations for same record. Coupon is changed regarding product, so i can be different for every record selected from database.

Answer 1

Can you not do this with a CROSS APPLY?

Answer 2

It's simple, computed value can be used by applying is value with cross apply

like this select cpk.coupon, p.Price, p.Price-cpk.coupon as FinalPrice -- etc

from Product -- etc
CROSS APPLY (
   select coupon = CASE 
  WHEN c.CouponPercent = 0 THEN p.Price - (c.CouponPercent/100)
  ELSE c.CouponValue
END as Coupon ) as cpk

where --etc