一、報表函數簡介：
回顧一下前面《Oracle開發專題之：窗口函數》中關于全統計一節，我們使用了Oracle提供的：
sum(sum(tot_sales)) over (order by month rows between unbounded preceding and unbounded following)
來統計全年的訂單總額，這個函數會在記錄集形成的過程中，每檢索一條記錄就執行一次，它總共執行了12次。這是非常費時的。實際上我們還有更簡便的方法：
SQL> select month,
2 sum(tot_sales) month_sales,
3 sum(sum(tot_sales)) over(order by month
4 rows between unbounded preceding and unbounded following) win_sales,
5 sum(sum(tot_sales)) over() rpt_sales
6 from orders
7 group by month;
MONTH MONTH_SALES WINDOW_SALES REPORT_SALES
---------- ----------- ------------ ------------
1 610697 6307766 6307766
2 428676 6307766 6307766
3 637031 6307766 6307766
4 541146 6307766 6307766
5 592935 6307766 6307766
6 501485 6307766 6307766
7 606914 6307766 6307766
8 460520 6307766 6307766
9 392898 6307766 6307766
10 510117 6307766 6307766
11 532889 6307766 6307766
12 492458 6307766 6307766
已選擇12行。
over函數的空括號表示該記錄集的所有記錄都應該被列入統計的范圍，如果使用了partition by則先分區，再依次統計各個分區。
二、RATIO_TO_REPORT函數：
報表函數特(窗口函數)特別適合于報表中需要同時顯示詳細數據和統計數據的情況。例如在銷售報告中經常會出現這樣的需求：列出上一年度每個月的銷售總額、年底銷售額以及每個月的銷售額占全年總銷售額的比例：
方法①:
select all_sales.*,
100 * round(cust_sales / region_sales, 2) || '%' Percent
from (select o.cust_nbr customer,
o.region_id region,
sum(o.tot_sales) cust_sales,
sum(sum(o.tot_sales)) over(partition by o.region_id) region_sales
from orders_tmp o
where o.year = 2001
group by o.region_id, o.cust_nbr) all_sales
where all_sales.cust_sales > all_sales.region_sales * 0.2;
這是一種笨方法也是最易懂的方法。
方法②：
select region_id, salesperson_id,
sum(tot_sales) sp_sales,
round(sum(tot_sales) / sum(sum(tot_sales))
over (partition by region_id), 2) percent_of_region
from orders
where year = 2001
group by region_id, salesperson_id
order by region_id, salesperson_id;
方法③
select region_id, salesperson_id,
sum(tot_sales) sp_sales,
round(ratio_to_report(sum(tot_sales))
over (partition by region_id), 2) sp_ratio
from orders
where year = 2001
group by region_id, salesperson_id
order by region_id, salesperson_id;