Sql server SQL Server:如何将CTE递归限制为刚刚递归添加的行? 简单的例子
让我们尝试一个更简单的示例,这样人们就可以了解这些概念,并有一个实用的示例,您可以将其复制并粘贴到SQL查询分析器中:Sql server SQL Server:如何将CTE递归限制为刚刚递归添加的行? 简单的例子,sql-server,common-table-expression,Sql Server,Common Table Expression,让我们尝试一个更简单的示例,这样人们就可以了解这些概念,并有一个实用的示例,您可以将其复制并粘贴到SQL查询分析器中: CREATE TABLE ##Nodes ( NodeID varchar(50) PRIMARY KEY NOT NULL, ParentNodeID varchar(50) NULL ) INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('A', null) INSERT INTO ##Nodes (NodeID,
CREATE TABLE ##Nodes
(
NodeID varchar(50) PRIMARY KEY NOT NULL,
ParentNodeID varchar(50) NULL
)
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('A', null)
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('B', 'A')
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('C', 'B')
想象一个具有继承权的节点表:
A
- B
- C
我们可以在查询分析器中开始测试:
CREATE TABLE ##Nodes
(
NodeID varchar(50) PRIMARY KEY NOT NULL,
ParentNodeID varchar(50) NULL
)
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('A', null)
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('B', 'A')
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('C', 'B')
所需输出:
ParentNodeID NodeID GenerationsRemoved
============ ====== ==================
NULL A 1
NULL B 2
NULL C 3
A B 1
A C 2
B C 1
现在,建议的CTE表达式的输出不正确:
WITH NodeChildren AS
(
--initialization
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM ##Nodes
WHERE ParentNodeID IS NULL
UNION ALL
--recursive execution
SELECT P.ParentNodeID, N.NodeID, P.GenerationsRemoved + 1
FROM NodeChildren AS P
INNER JOIN ##Nodes AS N
ON P.NodeID = N.ParentNodeID
)
SELECT ParentNodeID, NodeID, GenerationsRemoved
FROM NodeChildren
实际产出:
ParentNodeID NodeID GenerationsRemoved
============ ====== ==================
NULL A 1
NULL B 2
NULL C 3
注意:如果SQL Server 2005†CTE不能像我在2000年以前做的那样,那没关系,这就是答案。无论谁给出“这不可能”的答案都将赢得赏金。但我会等几天,以确保每个人都同意,这是不可能的,然后我无可挽回地给250的声誉,一个不解决我的问题
挑剔者角落
†不是2008年
‡不诉诸UDF*,这是我们已经拥有的解决方案
*除非您能在原始问题中找到改进UDF性能的方法
原始问题 我有一个节点表,每个节点都有一个指向另一个节点(或null)的父节点 举例说明:
1 My Computer
2 Drive C
4 Users
5 Program Files
7 Windows
8 System32
3 Drive D
6 mp3
我想要一个返回所有父子关系以及它们之间的代数的表
对于所有直接父关系:
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 1 1
1 2 1
2 4 1
2 5 1
2 7 1
1 3 1
3 6 1
7 8 1
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 2 2
(null) 3 2
1 4 2
1 5 2
1 7 2
1 6 2
2 8 2
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 4 3
(null) 5 3
(null) 7 3
(null) 6 3
1 8 3
但还有祖父母关系:
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 1 1
1 2 1
2 4 1
2 5 1
2 7 1
1 3 1
3 6 1
7 8 1
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 2 2
(null) 3 2
1 4 2
1 5 2
1 7 2
1 6 2
2 8 2
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 4 3
(null) 5 3
(null) 7 3
(null) 6 3
1 8 3
还有曾祖父祖母的关系:
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 1 1
1 2 1
2 4 1
2 5 1
2 7 1
1 3 1
3 6 1
7 8 1
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 2 2
(null) 3 2
1 4 2
1 5 2
1 7 2
1 6 2
2 8 2
ParentNodeID ChildNodeID GenerationsRemoved
============ =========== ===================
(null) 4 3
(null) 5 3
(null) 7 3
(null) 6 3
1 8 3
因此,我可以计算出基本的CTE初始化:
WITH (NodeChildren) AS
{
--initialization
SELECT ParentNodeID, NodeID AS ChildNodeID, 1 AS GenerationsRemoved
FROM Nodes
}
现在的问题是递归部分。当然,显而易见的答案是行不通的:
WITH (NodeChildren) AS
{
--initialization
SELECT ParentNodeID, ChildNodeID, 1 AS GenerationsRemoved
FROM Nodes
UNION ALL
--recursive execution
SELECT parents.ParentNodeID, children.NodeID, parents.Generations+1
FROM NodeChildren parents
INNER JOIN NodeParents children
ON parents.NodeID = children.ParentNodeID
}
Msg 253, Level 16, State 1, Line 1
Recursive member of a common table expression 'NodeChildren' has multiple recursive references.
生成整个递归列表所需的所有信息都存在于inital CTE表中。但如果不允许,我会尝试:
WITH (NodeChildren) AS
{
--initialization
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM Nodes
UNION ALL
--recursive execution
SELECT parents.ParentNodeID, Nodes.NodeID, parents.Generations+1
FROM NodeChildren parents
INNER JOIN Nodes
ON parents.NodeID = nodes.ParentNodeID
}
但这失败了,因为它不仅连接递归元素,而且不断递归地反复添加相同的行:
Msg 530, Level 16, State 1, Line 1
The statement terminated. The maximum recursion 100 has been exhausted before statement completion.
在SQL Server 2000中,我使用用户定义函数(UDF)模拟了一个CTE:
防止爆炸的魔法是限制条件:
其中CurrentParents.Generations-@Generations-1
如何防止递归CTE永远递归 旁白:你们有SQL Server 2008吗?这可能适用于。如果我理解您的意图,您可以通过这样做获得结果:
DECLARE @StartID INT;
SET @StartID = 1;
WITH CTE (ChildNodeID, ParentNodeID, [Level]) AS
(
SELECT t1.ChildNodeID,
t1.ParentNodeID,
0
FROM tblNodes AS t1
WHERE ChildNodeID = @StartID
UNION ALL
SELECT t1.ChildNodeID,
t1.ParentNodeID,
t2.[Level]+1
FROM tblNodes AS t1
INNER JOIN CTE AS t2 ON t1.ParentNodeID = t2.ChildNodeID
)
SELECT t1.ChildNodeID, t2.ChildNodeID, t1.[Level]- t2.[Level] AS GenerationsDiff
FROM CTE AS t1
CROSS APPLY CTE t2
这将返回所有节点之间的生成差异,您可以根据具体需要对其进行修改。好吧,您的答案不太明显:-) 这部分被称为递归CTE的“锚定”部分——但它实际上应该只从表中选择一行或几行——这将选择所有内容 我想你这里缺少的只是一个合适的WHERE子句:
WITH (NodeChildren) AS
{
--initialization
SELECT ParentNodeID, ChildNodeID, 1 AS GenerationsRemoved
FROM Nodes
**WHERE ParentNodeID IS NULL**
然而,我担心你的要求,不仅是“直”的层次结构,而且还有祖父母子女行,可能不是那么容易满足。。。。通常,递归CTE只会显示一个级别及其直接下属(当然,在层次结构中也是如此),它通常不会跳过一个、两个甚至更多级别
希望这有点帮助
Marc试试这个:
WITH Nodes AS
(
--initialization
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM ##Nodes
UNION ALL
----recursive execution
SELECT P.ParentNodeID, N.NodeID, P.GenerationsRemoved + 1
FROM Nodes AS P
INNER JOIN ##Nodes AS N
ON P.NodeID = N.ParentNodeID
WHERE P.GenerationsRemoved <= 10
)
SELECT ParentNodeID, NodeID, GenerationsRemoved
FROM Nodes
ORDER BY ParentNodeID, NodeID, GenerationsRemoved
将节点作为
(
--初始化
选择ParentNodeID、NodeID、1作为已删除的代
来自##节点
联合所有
----递归执行
选择P.ParentNodeID、N.NodeID、P.GenerationsRemoved+1
作为P从节点开始
作为N的内部联接##节点
在P.NodeID=N.ParentNodeID上
其中P.GenerationsRemoved问题在于Sql Server默认递归限制(100)。如果您在顶部尝试您的示例,删除了锚限制(也添加了Order By):
这将产生所需的结果。您面临的问题是,您将重复100次以上的行数较多,这是一个默认限制。这可以通过添加选项(最大递归x)来更改
在查询之后,其中x是一个介于1和32767之间的数字。x也可以设置为0,这不会设置任何限制,但可能会很快对服务器性能产生非常有害的影响。很明显,随着节点中的行数增加,递归数可能会很快增加,除非有限制,否则我将避免这种方法表中行的已知上限。为完整起见,最终查询应如下所示:
WITH NodeChildren AS
(
--initialization
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM Nodes
UNION ALL
--recursive execution
SELECT P.ParentNodeID, N.NodeID, P.GenerationsRemoved + 1
FROM NodeChildren AS P
inner JOIN Nodes AS N
ON P.NodeID = N.ParentNodeID
)
SELECT *
FROM NodeChildren
ORDER BY ParentNodeID
OPTION (MAXRECURSION 32767)
如果32767可以向下调整以适应您的场景您是否尝试在CTE中构建路径并使用它来识别祖先
然后可以从祖先节点深度中减去后代节点深度,以计算GenerationsRemoved列,如下所示
DECLARE @Nodes TABLE
(
NodeId varchar(50) PRIMARY KEY NOT NULL,
ParentNodeId varchar(50) NULL
)
INSERT INTO @Nodes (NodeId, ParentNodeId) VALUES ('A', NULL)
INSERT INTO @Nodes (NodeId, ParentNodeId) VALUES ('B', 'A')
INSERT INTO @Nodes (NodeId, ParentNodeId) VALUES ('C', 'B')
DECLARE @Hierarchy TABLE
(
NodeId varchar(50) PRIMARY KEY NOT NULL,
ParentNodeId varchar(50) NULL,
Depth int NOT NULL,
[Path] varchar(2000) NOT NULL
)
WITH Hierarchy AS
(
--initialization
SELECT NodeId, ParentNodeId, 0 AS Depth, CONVERT(varchar(2000), NodeId) AS [Path]
FROM @Nodes
WHERE ParentNodeId IS NULL
UNION ALL
--recursive execution
SELECT n.NodeId, n.ParentNodeId, p.Depth + 1, CONVERT(varchar(2000), p.[Path] + '/' + n.NodeId)
FROM Hierarchy AS p
INNER JOIN @Nodes AS n
ON p.NodeId = n.ParentNodeId
)
INSERT INTO @Hierarchy
SELECT *
FROM Hierarchy
SELECT parent.NodeId AS AncestorNodeId, child.NodeId AS DescendantNodeId, child.Depth - parent.Depth AS GenerationsRemoved
FROM @Hierarchy AS parent
INNER JOIN @Hierarchy AS child
ON child.[Path] LIKE parent.[Path] + '/%'
这打破了Chris Shaffer答案的递归限制
我创建了一个带有循环的表:
CREATE TABLE ##Nodes
(
NodeID varchar(50) PRIMARY KEY NOT NULL,
ParentNodeID varchar(50) NULL
)
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('A', 'C');
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('B', 'A');
INSERT INTO ##Nodes (NodeID, ParentNodeID) VALUES ('C', 'B');
在存在潜在循环的情况下(即ParentNodeId不为NULL),删除的生成从2开始。然后,我们可以通过检查(p.ParentNodeId==N.NodeID)来标识循环,我们只是不添加它。之后,我们附加省略的生成remove=1
WITH ParentNodes AS
(
--initialization
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM ##Nodes
WHERE ParentNodeID IS NULL
UNION ALL
SELECT P.ParentNodeID, N.NodeID, 2 AS GenerationsRemoved
FROM ##Nodes N
JOIN ##Nodes P ON N.ParentNodeID=P.NodeID
WHERE P.ParentNodeID IS NOT NULL
UNION ALL
----recursive execution
SELECT P.ParentNodeID, N.NodeID, P.GenerationsRemoved + 1
FROM ParentNodes AS P
INNER JOIN ##Nodes AS N
ON P.NodeID = N.ParentNodeID
WHERE P.ParentNodeID IS NULL OR P.ParentNodeID <> N.NodeID
),
Nodes AS (
SELECT ParentNodeID, NodeID, 1 AS GenerationsRemoved
FROM ##Nodes
WHERE ParentNodeID IS NOT NULL
UNION ALL
SELECT ParentNodeID, NodeID, GenerationsRemoved FROM ParentNodes
)
SELECT ParentNodeID, NodeID, GenerationsRemoved
FROM Nodes
ORDER BY ParentNodeID, NodeID, GenerationsRemoved
将ParentNodes作为
(
--初始化
选择ParentNodeID、NodeID、1作为已删除的代
来自##节点
其中ParentNodeID为NULL
联合所有
选择P.ParentNodeID、N.NodeID、2作为已删除的生成
从##节点N
连接N.ParentNodeID=P.NodeID上的##节点P
其中P.ParentNodeID不为NULL
联合所有
----递归执行
选择P.ParentNodeID、N.NodeID、P.GenerationsRemoved+1
从ParentNodes作为P
作为N的内部联接##节点
在P.NodeID=N.ParentNodeID上
其中P.ParentNodeID为NULL或P.ParentNodeID N.NodeID
),
节点作为(
选择ParentNodeID、NodeID、1作为已删除的代
来自##节点
其中ParentNodeID不为NULL
联合所有
选择ParentNodeID、NodeID、GenerationsRemoved FROM ParentNodes
)
选择ParentNodeID、NodeID、GenerationsRemoved
从节点
按父项排序NodeID、NodeID、GenerationsRemoved
,其中cte为
(
选择a=65,L=1