Oracle具有

Oracle has a good array of date manipulation functions. The two pertinent ones for this problem are

• 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

• MONTHS_BETWEEN() which calculates the number of months between two dates
• ADD_MONTHS() which increments a date by the given number of months

我们可以结合使用这些功能来生成一张表格，其中包含您的表格记录所涵盖的所有月份.然后，我们使用外部联接将有条件的记录从USER_INFO联接到该日历.当没有记录匹配时， count(id)将为零.

We can combine these functions to generate a table of all the months spanned by your table's records. Then we use an outer join to conditionally join records from USER_INFO to that calendar. When no records match count(id) will be zero.

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
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