如何添加将按正确顺序显示的日期（月份），现在它在递归 CTE SQL 中倒退

Question

with recursive cte (id, qty) (
    select id, qty from mytable
    union all
    select id, qty - 1 from cte where qty > 1
)
select id from cte order by id

问题：

如何添加按正确顺序显示的日期（月），现在它在递归 CTE 中倒退？

with recursive cte (id, qty, Forecast_date) 
( 
select id, qty, StartDate from mytable 
union all 
select id, qty - 1, eomonth(dateadd(month, 1,Forecast_date)) from cte where qty > 1 ) 

select id,Forecast_date from cte order by id

输出：

9/30/2023   0
8/31/2023   1
7/31/2023   2
6/30/2023   3
5/31/2023   4
4/30/2023   5
3/31/2023   6
2/28/2023   7
1/31/2023   8
12/31/2022  9
11/30/2022  10
10/31/2022  11
9/30/2022   12
8/31/2022   13
7/31/2022   14
6/30/2022   15
5/31/2022   16
...

预计增量从 2022 年 5 月 31 日开始，而不是从 2023 年 9 月 30 日开始，这应该是最后一条记录

获得积分：

Id  Forecast_date  qty
1   5/31/2022      0
2   6/30/2022      1

Answer 1

从生成递增序列开始，然后在外部查询中进行计算可能更简单：

with recursive cte (id, qty, forecast_date, lvl) (
    select id, qty, datefromparts(year(forecast_date), month(forecast_date), 1), 0 lvl from mytable
    union all
    select id, qty, forecast_date, lvl + 1 from cte where lvl < qty
)
select 
    id,
    qty - lvl as dty,
    eomonth(dateadd(month, -lvl, forecast_date)) new_forecast_date
from cte
order by id, new_forecast_date

月末计算很棘手：您不能通过添加月份从月末跳到另一个月末，因为并非所有月的天数都相同。所以查询使用开始月份的开始进行计算，then 使用 eomonth().

Answer 2

减去种子中的月数Select:

with recursive cte (id, qty, Forecast_date) 
(
select id, qty, eomonth(dateadd(month, -qty,StartDate)) 
from mytable 
union all 
select id, qty - 1, eomonth(dateadd(month, 1,Forecast_date)) 
from cte 
where qty >= 1 
) 

select * 
from cte 
order by id, qty

或添加另一列，从数量 0 开始并向上计数而不是向下计数：

with recursive cte (id, qty, Forecast_date, stopat)
( 
select id, 0, StartDate, qty
from mytable 
union all 
select id, qty + 1, eomonth(dateadd(month, 1,Forecast_date)), stopat
from cte 
where qty < stopat 
) 

select id, qty, Forecast_date
from cte 
order by id, qty

如何添加将按正确顺序显示的日期（月份），现在它在递归 CTE SQL 中倒退

How to add Date(month) that will show in right order, right now it goes backward in recursion CTE SQL

sql

date

recursive-query