Trigger for adding the value in the sql field

There are tables: Product and Implementation. I want to make a trigger to change the value in the Quantity field in the table. Implementation. After the change, the trigger should multiply the "Price Purchase" by the value in the "Quantity" of the Implementation table and insert the resulting value into the "Sales Amount". I have thought of this option so far: create trigger planSALE after update on Number for each row begin update Implementation_ set SumSales = Quantity * PricePurchase; end;