member function to get the sum in oracle - oracle

Question

I have a type called sell_type defined as
CREATE OR REPLACE TYPE sell_type AS OBJECT (
dname VARCHAR (50),
car_model VARCHAR(20),
make VARCHAR (20),
price NUMBER (10,2),
MEMBER FUNCTION total_sales RETURN NUMBER
);
/
Body:
CREATE OR REPLACE TYPE BODY sell_type AS
MEMBER FUNCTION total_sales RETURN NUMBER IS
BEGIN
RETURN SELF.price;
END total_sales;
END;
/
And an object table
CREATE TABLE sell of Sell_Type;
/
I want to get the total sales for a given seller with something like:
select s.total_sales() from sell s
where s.dname = 'John Doe';
But what I get is a separate list of prices of all the sales of that given seller, rather than the total of those prices.
I know that I have to fix my type body somehow. I tried to use the SUM() inside the return but that didn't work. Can someone please help?

Answer 1

Summing is an aggregation, a set function. A Type is a single thing; it is not possible for a Type instance to execute an aggregation across all the instances of its peers.
If you want to do such a thing you would need to declare a new type, with a signature like this:
CREATE OR REPLACE TYPE sell_set AS OBJECT (
sell_items sell_type,
MEMBER FUNCTION total_sales (p_seller varchar2) RETURN NUMBER
);
/
Writing the body for this type is left as an exercise for the reader ;-)
Note that Oracle SQL and PL/SQL do work with OO concepts but in a clunky fashion. It's fine to explore the syntax for educational purposes, if only to learn its limitations. But there are a very narrow set of use cases in real life. A relational data model is the far superior way of storing data.

Answer 2

This body will do the trick. But it will return the same value for each row on the sell table. Therefore, you have to use 'group by' or 'max()' if you want to see just one row of result.
CREATE OR REPLACE
TYPE BODY SELL_TYPE AS
MEMBER FUNCTION total_sales (p_seller varchar2) RETURN NUMBER IS
total_price NUMBER;
BEGIN
SELECT sum(s.price) INTO total_price FROM sell s where s.dname = p_seller;
RETURN total_price;
END total_sales;
END;
/
select query will look like this.
select s.total_sales('John')
from sell s GROUP BY s.total_sales('John');