How to SUM every row for SubTotal?

[The Nice Spider]

 If I have table like:
 
 CODE QTY
 100      30
 200      20
 300      25
 
 and I want a result like:
 
 CODE QTY SUBTOTAL
100      30     30 
 200      20     50   (this come from 30+20)
300      25     75   (this come from 50+25)
 
 How to write query like that?

                
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