如何按月分组，包括所有月份？

Question

我 table 按月分组

  SELECT TO_CHAR (created, 'YYYY-MM') AS operation, COUNT (id)
    FROM user_info
   WHERE created IS NOT NULL
GROUP BY ROLLUP (TO_CHAR (created, 'YYYY-MM'))

2015-04 1
2015-06 10
2015-08 22
2015-09 8
2015-10 13
2015-12 5
2016-01 25
2016-02 37
2016-03 24
2016-04 1
2016-05 1
2016-06 2
2016-08 2
2016-09 7
2016-10 103
2016-11 5
2016-12 2
2017-04 14
2017-05 2
        284

但记录并未涵盖所有月份。
我希望输出包括所有月份，输出中显示缺失的月份并使用默认值：

2017-01 ...
2017-02 ...
2017-03 ZERO
2017-04 ZERO
2017-05 ...

Answer 1

Oracle 有 a good array of date manipulation functions。这个问题的两个相关问题是

MONTHS_BETWEEN() 计算两个日期之间的月数
ADD_MONTHS() 将日期增加给定的月数

我们可以结合这些函数来生成 table 您的 table 记录跨越的所有月份。然后我们使用外部联接有条件地将 USER_INFO 中的记录联接到该日历。当没有记录匹配时 count(id) 将为零。

with cte as (
  select max(trunc(created, 'MM')) as max_dt
         , min(trunc(created, 'MM')) as min_dt
  from user_info
  )
 , cal as (
    select add_months(min_dt, (level-1)) as mth
    from cte
    connect by level <= months_between(max_dt, min_dt) + 1
)
select to_char(cal.mth, 'YYYY-MM') as operation
       , count(id)
from  cal
     left outer join user_info
   on trunc(user_info.created, 'mm') = cal.mth
group by rollup (cal.mth)
order by 1
/

如何按月分组，包括所有月份？

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