SQL & PL/SQL

I am very curios to know why we have to hard-code the "pivot in" clause in a pivot query. Does this not defeat the purpose of pivoting?

we have to write this:

SELECT *
FROM (SELECT customer_id, product_code, quantity
FROM pivot_test)
PIVOT (SUM(quantity) AS sum_quantity FOR (product_code) IN ('A' AS a, 'B' AS b, 'C' AS c))
ORDER BY customer_id;

Why can we not put a subquery in the "IN" clause? Or even better, leave it blank to indicate we are pivoting for all.

I know you can do something like this with the PIVOT XML function, but I want columns in the result, not XML. And I also do not want to build the query as a string and execute it like that, it gets really messy and I feel sorry for the next bloke who needs to take over from me.

Does anybody know why this seems to not be possible for ORACLE?

Thanks all.