Oracle Reporting 1 - Ratio_to_Report Function

The RATIO_TO_REPORT function computes the ratio of a value to the sum of a set of values. RATIO_TO_REPORT ( expr ) OVER ( [query_partition_clause] ).
In this series of articles, I'm using Oracle's SH schema. It is modeled in star schema. The following query returns top 3 best-selling products in 2000, their sales amount, percentage of total amount, and the rank.

select * from (SELECT prod.prod_name, TO_CHAR(SUM(amount_sold),'9,999,999,999') "SALES($)",to_char(RATIO_TO_REPORT(SUM(amount_sold)) OVER () * 100, '99.99' ) || '%' Percentage_of_Taotal_Amount,rank() over(order by sum(amount_sold) desc) rankFROM sales s, products prodWHERE s.prod_id=prod.prod_id AND trunc(s.time_id,'yyyy')=to_DATE('01-JAN-2000')GROUP BY (prod.prod_name))where rank < br style='font-size:12px;font-style:normal;font-weight:normal;color:rgb(102, 102, 102);'

Ratio_to_report() Performance Analysis:
Consider this query:

WITH channel_summary AS (  SELECT channels.channel_desc, SUM(amount_sold)    AS channel_total FROM sales, channels    WHERE sales.channel_id = channels.channel_id GROUP BY channels.channel_desc)  SELECT channel_desc, channel_total  FROM channel_summary WHERE channel_total < (SELECT SUM(channel_total) * 1/3  FROM channel_summary); 

Statistics
----------------------------------------------------------
          2  recursive calls
          8  db block gets
       1730  consistent gets
          1  physical reads
        864  redo size

        622  bytes sent via SQL*Net to client

        523  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          1  rows processed

Oracle needs to use temp tablespace to save the data of with-clause, that's the reason of 2 recursive calls and 864 redo size. However, we can eliminate the writes to/reads from temp tablespace by using ratio_to_report. 
Both queries run twice to avoid the effect of hard-parse.

SELECT channel_desc, amount_sold FROM ( SELECT ch.channel_desc, sum(s.amount_sold) amount_sold, ratio_to_report(sum(s.amount_sold)) over() ratio  FROM channels ch, sales s WHERE ch.channel_id=s.channel_id  GROUP BY ch.channel_desc) WHERE ratio <= 0.33;

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       1721  consistent gets
          0  physical reads
          0  redo size
        620  bytes sent via SQL*Net to client
        523  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
          1  rows processed