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) rank
FROM sales s, products prod
WHERE s.prod_id=prod.prod_id 
AND trunc(s.time_id,'yyyy')=to_DATE('01-JAN-2000')
GROUP BY (prod.prod_name)
)
where rank <= 3;

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

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

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