SQL 服务器 - CTE 内的 CTE

Question

I have this query:

WITH months(dt) AS 
   (SELECT DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1) AS dt 
    UNION ALL
    SELECT dateadd(month, -1, dt)
    FROM months)
SELECT 
top (datediff(month, '2020-01-01', DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1)) + 1) 
YEAR(months.dt) yr, MONTH(months.dt) mnth
FROM months
OPTION (maxrecursion 0);

What I need is that the last Select result is a CTE expression so I can use it on other select.

I have tried this:

WITH months(dt) AS 
   (SELECT DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1) AS dt 
    UNION ALL
    SELECT dateadd(month, -1, dt)
    FROM months),
    cte2 as (
SELECT 
top (datediff(month, '2020-01-01', DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1)) + 1) 
YEAR(months.dt) yr, MONTH(months.dt) mnth
FROM months
OPTION (maxrecursion 0)
)

But I get an error, Im doing something wrong for sure.

Any advice?

Answer 1

You're almost there. You need to add the final SELECT over cte2 . For example:

WITH 
months (dt) AS 
   (SELECT DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1) AS dt 
    UNION ALL
    SELECT dateadd(month, -1, dt)
    FROM months),
cte2 as (
    SELECT 
    top (datediff(month, '2020-01-01', 
           DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1)) + 1) 
    YEAR(months.dt) yr, MONTH(months.dt) mnth
    FROM months
)
SELECT * from cte2
OPTION (maxrecursion 0)

This way you can chain two, three, four, etc CTEs one after the other. Any CTE can JOIN, use, or combine any of the CTEs defined previously.