如何在SQL中存儲遞歸CTE的結果？

Question

如果我有這樣的遞歸CTE，如何將結果存儲在變量中？

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)

我嘗試了以下操作，但是SSMS抱怨這兩個選項的語法：

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))

和

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))

Answer 1

您可以先聲明變量，然后分配它：

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);