Which query will run faster

Question

Hi,
I have following two tables:
SQL> desc customers
Name Null? Type
ID NOT NULL NUMBER
NAME VARCHAR2(20)
SQL> desc orders
Name Null? Type
CUST_ID NUMBER
ARTICLE_NR VARCHAR2(20)
PRICE NUMBER(5,2)
I want to find each customer's order with the highest price along with its respective article number and the customer's name.
Please let me know, which of the following query will work fast and why:
SELECT c.NAME, o.article_nr, o.price
FROM customers c,
(SELECT cust_id, article_nr, price,
ROW_NUMBER () OVER (PARTITION BY cust_id ORDER BY price DESC)
r
FROM orders) o
WHERE o.r = 1 AND c.ID = o.cust_id
SELECT NAME, article_nr, price
FROM orders o, customers c
WHERE c.ID = o.cust_id
AND (o.cust_id, price) IN (SELECT cust_id, MAX (price)
FROM orders
GROUP BY cust_id);
Thanks.

Answer 1

Your second version is selecting twice from the same table (orders). The first version needs only one read over this table. So there is a good chance that the first version is faster than the second.
However there is always a possibility depending on indexes etc. that it is otherwise.