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Accepted
Ashish
Asked: 2012-04-06 02:29:29 +0800 CST

CTE 在无限循环中运行

  • 772

我的 CTE 为特定客户无限循环运行，我无法找出原因。

这是查询：

;WITH ClassTree
           AS (SELECT ID, NAME, Parent_ID
               FROM   TableName
               WHERE  ID = 1
               UNION ALL
               SELECT T.ID, T.NAME, T.Parent_ID
               FROM   TableName T WITH (NOLOCK)
                      JOIN ClassTree
                        ON Parent_ID = ClassTree.ID
)
SELECT * FROM ClassTree
sql-server cte

3 个回答

  1. 这里有一些东西可以用来找到你的周期。

    declare @T table
(
  ID int,
  Parent_ID int
)

insert into @T values
(1, 3),(2, 1),(3, 2),    -- This is a cycle
(4, 4),                  -- This is a cycle
(5, null),(6, 5),(7, 6)  -- This is not a cycle

;with C as
(
  select T.ID,
         T.Parent_ID,
         cast(',' + cast(ID as varchar(10)) + ',' as varchar(max)) as Path,
         0 Cycle
  from @T as T
  union all
  select T.ID,
         T.Parent_ID,
         C.Path + cast(T.ID as varchar(10)) + ',',
         case when C.Path like '%,'+cast(T.ID as varchar(10))+',%' 
           then 1 
           else 0 
         end
  from @T as T
    inner join C  
      on T.Parent_ID = C.ID
  where C.Cycle = 0
)
select *
from C
where Cycle = 1

    结果：

    ID          Parent_ID   Path       Cycle
----------- ----------- ---------- -----------
4           4           ,4,4,      1
3           2           ,3,1,2,3,  1
2           1           ,2,3,1,2,  1
1           3           ,1,2,3,1,  1
    • 8
  2. Best Answer

    我认为这应该为您找到问题记录。它将 a 添加LEVEL到您的层次结构中，然后查找存在于多个级别的单个 ID 记录。

    ;WITH ClassTree
           AS (SELECT ID, NAME, Parent_ID, 1 as 'Level'
               FROM   TableName
               WHERE  ID = 1
               UNION ALL
               SELECT T.ID, T.NAME, T.Parent_ID, Level + 1 as 'Level'
               FROM   TableName T WITH (NOLOCK)
                      JOIN ClassTree
                        ON Parent_ID = ClassTree.ID
)

SELECT *
FROM ClassTree c1
WHERE EXISTS (SELECT 1 FROM ClassTree c2
              WHERE c2.id = c1.id
              AND c2.Level > c1.level)
    • 3

  3. 我要做的第一件事就是改变这个：

    JOIN ClassTree
     ON Parent_ID = ClassTree.ID

    对此：

    JOIN ClassTree                         
     ON t.Parent_ID = ClassTree.ID

    它可能正在尝试将 ClassTree 连接到自身，因为您没有在连接中指定表别名。

    • 1

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