Question

在Oracle 11g中，我有一个名为ITEM的表，其中每条记录分为maingroup和subgroup，如下所示：

+-------+---------+----------+
 item_id maingroup subgroup
+-------+---------+---------+
       1 group1    subgroup1
       2 group1    subgroup2
       3 group2    subgroup1
       4 group2    subgroup2
 ...

我必须编写一个程序来报告表ITEM中的项目数。报告输出与此类似：

                 subgroup1   subgroup2   group_total
group1                  10           5            15
group2                   0           1             1
subgroup_total          10           6            16

为此，我将编写一个SQL来查询数据，然后使用Java重新格式化输出。 SQL应该自己生成完整的报告，即我将仅使用Java重新格式化输出而不进行任何计算。所以，我决定SQL的输出应该是这样的：

+--------------+-----------+-----+
 maingroup      subgroup    cnt
+--------------+-----------+-----+ 
 group1         subgroup1      10
 group1         subgroup2       5
 group1         group_total    15
 group2         subgroup1       0
 group2         subgroup2       1
 group2         group_total     1
 subgroup_total subgroup1      10
 subgroup_total subgroup2       6
 subgroup_total group_total    16

理想情况下，SQL就像

一样简单

select maingroup, subgroup, count(*) cnt from ITEM 
group by maingroup, subgroup union all
select maingroup, 'group_total' as subgroup, count(*) cnt from ITEM
group by maingroup union all
select 'subgroup_total' as maingroup, subgroup, count(*) cnt from ITEM
group by subgroup;

但不，我简化了表格ITEM使问题易于理解，实际上，为了弥补这个ITEM，我必须使用一个大的子查询，所以它实际上是看起来像

select maingroup, subgroup, count(*) cnt from 
       (select maingroup, subgroup from ...) ITEM 
group by maingroup, subgroup union all
select maingroup, 'group_total' as subgroup, count(*) cnt from 
       (select maingroup, subgroup from ...) ITEM 
group by maingroup union all
select 'subgroup_total' as maingroup, subgroup, count(*) cnt from
       (select maingroup, subgroup from ...) ITEM 
group by subgroup;

使用相同的大子查询3次。我希望我可以重用此子查询，但我没有权限创建表或使用WITH子句。 是否可以重新排列上述SQL，以便子查询ITEM只处理一次而不创建临时表或使用WITH子句？

Answer 1

尝试使用grouping sets子句进行查询：

SELECT coalesce( maingroup, 'subgroup_total' ) As maingroup,
       coalesce( subgroup, 'group_total' ) As subgroup,
       count(*) cnt 
FROM very_complex_subquery
GROUP BY GROUPING SETS((maingroup, subgroup), (maingroup), (subgroup))
order by 1,2
;

演示：http://sqlfiddle.com/#!4/8ed9b/4

不使用Oracle数据库中的临时表或WITH子句重用子查询

1 个答案: