Oracle开发之报表函数

一、回顾一下前面《Oracle开发之窗口函数》中关于全统计一节，我们使用了Oracle提供的：

sum(sum(tot_sales)) over (order by month rows between unbounded preceding and unbounded following)

来统计全年的订单总额，这个函数会在记录集形成的过程中，每检索一条记录就执行一次，它总共执行了12次。这是非常费时的。实际上我们还有更简便的方法：

SQL> select month,
         sum(tot_sales) month_sales,
         sum(sum(tot_sales)) over(order by month
         rows between unbounded preceding and unbounded following) win_sales,
         sum(sum(tot_sales)) over() rpt_sales
    from orders
   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

已选择12行。

over函数的空括号表示该记录集的所有记录都应该被列入统计的范围，如果使用了partition by则先分区，再依次统计各个分区。

二、RATIO_TO_REPORT函数：

报表函数特(窗口函数)特别适合于报表中需要同时显示详细数据和统计数据的情况。例如在销售报告中经常会出现这样的需求：列出上一年度每个月的销售总额、年底销售额以及每个月的销售额占全年总销售额的比例：

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;

这是一种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;

Oracle提供的Ratio_to_report函数允许我们计算每条记录在其对应记录集或其子集中所占的比例。