Question

I’m stuck on a the type of trigger needed to for this constraint.

I will have a price and a commission. The price determines the commission amount, < 100 – 4%, < 200 – 5% etc.

My idea.
the database contains a separate table that will hold 4 price values , 101, 201, 401, 601, with their own matching comission %, this will be called PC. When I create a property listing I want to calculate the commission they earn depending on the price entered.

on insert, I need to check the new.price and compare it to the prices in PC. Once new.price is less than the price tuple, I set the price to that commission value

create or replace TRIGGER findCommission BEFORE INSERT OR UPDATE ON HASLISTING
FOR each ROW
BEGIN
IF (:NEW.ASKING_PRICE < 100001) THEN
:NEW.COMMISSION = 6.0;
END IF;
IF (:NEW.ASKING_PRICE < 250001) THEN
:NEW.COMMISSION = 5.5;
END IF;
IF (:NEW.ASKING_PRICE < 1000001) THEN
:NEW.COMMISSION = 5.0;
END IF;
IF (:NEW.ASKING_PRICE > 1000000) THEN
:NEW.COMMISSION = 4.0;
END IF;
END;

Answer 1

I would suggest using a function for calculations like this and then call it in the trigger. That way the commission logic stays seperate and can be changed.

Also, your commission table description might help.

create table price_comm(
   max_price number(20),
   comm number(5,2)
);


insert into price_comm (max_price, comm) values (10000, 2.0);
insert into price_comm (max_price, comm) values (20000, 3.0);
insert into price_comm (max_price, comm) values (30000, 4.0);
commit;

create or replace function f_get_comm_percent(
    i_price in number
) return number
as
 o_comm_percent price_comm.comm%type;
begin
  select comm 
    into o_comm_percent
  from (
      select comm,
             rank () over (order by max_price desc) rnk
        from price_comm
        where max_price <= i_price
  ) where rnk = 1;      

  return o_comm_percent;

end;
/

–this is also assuming that the ranges do not overlap and if they do, they get the maximum commision 😉

Now to get the commission values…

SQL> select f_get_comm_percent(12000) from dual;

F_GET_COMM_PERCENT(12000)
-------------------------
                        2

SQL> select f_get_comm_percent(45000) from dual;

F_GET_COMM_PERCENT(45000)
-------------------------
                        4

— and your trigger definition could be as simple as this. Looking at your question, it seems you have the percentage in the table and you need the commission value in your final table.

create or replace trigger trg_biu_haslisting
before insert or update of haslisting
for each row
referencing new as new and old as old
begin
  :NEW.commission := :NEW.price*f_get_comm_percent(:NEW.price);
  --any other columns that you need to set
end;
/

I haven’t tested the trigger code for syntax errors, please test on your end.