在特定条件下中断 CTE SQL 查询

Question

我有以下 SQL Server CTE 查询：

  ;with x
 as (
    select childref, 0 as lvl
    from [dbo].[TOMatriX]
    where parentref = @parentref

    union all

    select m.childref, x.lvl+1
    from [dbo].[TOMatriX] m
    inner join x on m.parentref = x.childref
)
select
    lvl [Level],
count(*) [Count], 
    stuff((select ', ' + CAST(ChildRef AS CHAR(9))
           from x t2 where t1.lvl = t2.lvl 
           for xml path('')),
          1,2,'') [Members]
from x t1
group by lvl

我只需要获取最高 12 级的详细信息，因此我将上述查询修改为：

;with x
 as (
    select childref, 0 as lvl
    from [dbo].[TOMatriX]
    where parentref = @parentref

    union all

    select m.childref, x.lvl+1
    from [dbo].[TOMatriX] m
    inner join x on m.parentref = x.childref
)
select top 12
    lvl [Level],
count(*) [Count], 
    stuff((select ', ' + CAST(ChildRef AS CHAR(9))
           from x t2 where t1.lvl = t2.lvl 
           for xml path('')),
          1,2,'') [Members]
from x t1
group by lvl

但是我如何使用 OPTION (maxrecursion) 来打破第 12 级的递归，我无法在我的查询中使用 maxrecursion 选项，我确实尝试如下使用它：

;with x
 as (
    select childref, 0 as lvl
    from [dbo].[TOMatriX]
    where parentref = 100000001

    union all

    select m.childref, x.lvl+1
    from [dbo].[TOMatriX] m
    inner join x on m.parentref = x.childref
)
select 
    lvl [Level],
count(*) [Count], 
    stuff((select ', ' + CAST(ChildRef AS CHAR(9))
           from x t2 where t1.lvl = t2.lvl 
           for xml path('')),
          1,2,'') [Members]
from x t1
group by lvl
OPTION (MAXRECURSION 12);

但我收到以下错误：

语句终止。在语句完成之前，最大递归 12 已经用完。

那么，如何使用 OPTION (maxrecursion) 来停止第 12 级的递归，就像在 2nd Query 中使用 TOP 一样。

注意：

的表结构

    TABLE [dbo].[TOMatriX](

        [ParentRef] [int] NOT NULL,
        [ChildRef] [int] NOT NULL,
-- Some Other Columns as well ...

)

如果可能，请提出任何性能改进建议。

Answer 1

以下是您如何设置限制条件的示例：

with x as (
      select childref, 0 as lvl
      from [dbo].[TOMatriX]
      where parentref = 100000001
      union all
      select m.childref, x.lvl+1
      from [dbo].[TOMatriX] m inner join
           x
           on m.parentref = x.childref
      where x.lvl <= 12
     )