如何将递归 CTE 的结果存储在 SQL 中?

How can I store the result of a recursive CTE in SQL?

如果我有这样的递归 CTE,如何将结果存储在变量中?

WITH MyCTE (ChildID, ParentID)
AS
(
   SELECT ID, ParentID From MyTable
    WHERE ID = 1
   UNION ALL
    SELECT MT.ID, MT.ParentID 
    FROM MyCTE Child
    JOIN MyTable MT ON MT.ID = Child.ParentID
    WHERE Child.ParentID IS NOT NULL
)
SELECT COUNT(*)
FROM MyCTE
OPTION (MAXRECURSION 20)

我尝试了以下方法,但 SSMS 抱怨两个选项中的语法:

DECLARE @numberOfRecords int = (
WITH MyCTE (ChildID, ParentID)
AS
(
   SELECT ID, ParentID From MyTable
    WHERE ID = 1
   UNION ALL
    SELECT MT.ID, MT.ParentID 
    FROM MyCTE Child
    JOIN MyTable MT ON MT.ID = Child.ParentID
    WHERE Child.ParentID IS NOT NULL
)
SELECT COUNT(*)
FROM MyCTE
OPTION (MAXRECURSION 20))

WITH MyCTE (ChildID, ParentID)
AS
(
   SELECT ID, ParentID From MyTable
    WHERE ID = 1
   UNION ALL
    SELECT MT.ID, MT.ParentID 
    FROM MyCTE Child
    JOIN MyTable MT ON MT.ID = Child.ParentID
    WHERE Child.ParentID IS NOT NULL
)
DECLARE @numberOfRecords int = (
SELECT COUNT(*)
FROM MyCTE
OPTION (MAXRECURSION 20))

可以先声明变量再赋值:

DECLARE @numberOfRecords int;

WITH MyCTE (ChildID, ParentID) AS (
      SELECT ID, ParentID
      FROM MyTable
      WHERE ID = 1
      UNION ALL
      SELECT MT.ID, MT.ParentID 
      FROM MyCTE Child JOIN
           MyTable MT
           ON MT.ID = Child.ParentID
      WHERE Child.ParentID IS NOT NULL
     )
SELECT @numberOfRecords = COUNT(*)
FROM MyCTE
OPTION (MAXRECURSION 20);