累積分析関数を使用してクエリにゼロ値レコードを追加する

CURRENT ROWの代わりに、PRECEDINGキーワードを使用して、前の行まで合計することができます。

with data as (
  select 1 id, 'A' name, 'fruit' r_group, '2007' year, '04' month, 5 sales from dual union all
  select 2 id, 'Z' name, 'fruit' r_group, '2007' year, '04' month, 99 sales from dual union all
  select 3 id, 'A' name, 'fruit' r_group, '2008' year, '05' month, 10 sales from dual union all
  select 4 id, 'B' name, 'vegetable' r_group, '2008' year, '07' month, 20 sales from dual )
select t.*, 
  coalesce(sum(sales) over (partition by  r_group order by year, month rows between unbounded preceding and 1 preceding),0) opening,
  sum(sales) over (partition by  r_group order by year, month rows between unbounded preceding and current row) closing
from (
  select year, month, r_group, sum(sales) sales
  from data
  group by year, month, r_group
  ) t
order by 3,1,2;

year    month   r_group     sales   opening closing
---------------------------------------------------
2007    04      fruit       104     0       104
2008    05      fruit       10      104     114
2008    07      vegetable   20      0       20