创建和使用 CTE 的指南

下列指南应用于非递归 CTE。有关适用于递归 CTE 的指南，请参阅后面的“定义和使用递归 CTE 的指南”。

CTE 之后必须跟随引用部分或全部 CTE 列的 SELECT、INSERT、UPDATE 或 DELETE 语句。也可以在 CREATE VIEW 语句中将 CTE 指定为视图中 SELECT 定义语句的一部分。
可以在非递归 CTE 中定义多个 CTE 查询定义。定义必须与以下集合运算符之一结合使用：UNION ALL、UNION、INTERSECT 或 EXCEPT。
CTE 可以引用自身，也可以引用在同一 WITH 子句中预先定义的 CTE。不允许前向引用。
不允许在一个 CTE 中指定多个 WITH 子句。例如，如果 CTE_query_definition 包含一个子查询，则该子查询不能包括定义另一个 CTE 的嵌套的 WITH 子句。
不能在 CTE_query_definition 中使用以下子句：
- COMPUTE 或 COMPUTE BY
- ORDER BY（除非指定了 TOP 子句）
- INTO
- 带有查询提示的 OPTION 子句
- FOR XML
- FOR BROWSE
如果将 CTE 用在属于批处理的一部分的语句中，那么在它之前的语句必须以分号结尾。
可以使用引用 CTE 的查询来定义游标。
可以在 CTE 中引用远程服务器中的表。
在执行 CTE 时，任何引用 CTE 的提示都可能与该 CTE 访问其基础表时发现的其他提示相冲突，这种冲突与引用查询中的视图的提示所发生的冲突相同。发生这种情况时，查询将返回错误。有关详细信息，请参阅视图解析。

定义和使用递归 CTE 指南

下列指南适用于定义递归 CTE 的情况：

递归 CTE 定义至少必须包含两个 CTE 查询定义，一个定位点成员和一个递归成员。可以定义多个定位点成员和递归成员；但必须将所有定位点成员查询定义置于第一个递归成员定义之前。所有 CTE 查询定义都是定位点成员，但它们引用 CTE 本身时除外。
定位点成员必须与以下集合运算符之一结合使用：UNION ALL、UNION、INTERSECT 或 EXCEPT。在最后一个定位点成员和第一个递归成员之间，以及组合多个递归成员时，只能使用 UNION ALL 集合运算符。
定位点成员和递归成员中的列数必须一致。
递归成员中列的数据类型必须与定位点成员中相应列的数据类型一致。
递归成员的 FROM 子句只能引用一次 CTE expression_name。
在递归成员的 CTE_query_definition 中不允许出现下列项：
- SELECT DISTINCT
- GROUP BY
- HAVING
- 标量聚合
- TOP
- LEFT、RIGHT、OUTER JOIN（允许出现 INNER JOIN）
- 子查询
- 应用于对 CTE_query_definition 中的 CTE 的递归引用的提示。

下列指南适用于使用递归 CTE：

无论参与的 SELECT 语句返回的列的为空性如何，递归 CTE 返回的全部列都可以为空。
如果递归 CTE 组合不正确，可能会导致无限循环。例如，如果递归成员查询定义对父列和子列返回相同的值，则会造成无限循环。可以使用 MAXRECURSION 提示以及在 INSERT、UPDATE、DELETE 或 SELECT 语句的 OPTION 子句中的一个 0 到 32,767 之间的值，来限制特定语句所允许的递归级数，以防止出现无限循环。这样就能够在解决产生循环的代码问题之前控制语句的执行。服务器范围内的默认值是 100。如果指定 0，则没有限制。每一个语句只能指定一个 MAXRECURSION 值。有关详细信息，请参阅查询提示 (Transact-SQL)。
不能使用包含递归公用表表达式的视图来更新数据。
可以使用 CTE 在查询上定义游标。递归 CTE 只允许使用快速只进游标和静态（快照）游标。如果在递归 CTE 中指定了其他游标类型，则该类型将转换为静态游标类型。
可以在 CTE 中引用远程服务器中的表。如果在 CTE 的递归成员中引用了远程服务器，那么将为每个远程表创建一个假脱机，这样就可以在本地反复访问这些表。

参数

expression_name

公用表表达式的有效标识符。 expression_name 必须与在同一 WITH <common_table_expression> 子句中定义的任何其他公用表表达式的名称不同，但 expression_name 可以与基表或基视图的名称相同。在查询中对 expression_name 的任何引用都会使用公用表表达式，而不使用基对象。

column_name

在公用表表达式中指定列名。在一个 CTE 定义中不允许出现重复的名称。指定的列名数必须与 CTE_query_definition 结果集中列数匹配。只有在查询定义中为所有结果列都提供了不同的名称时，列名称列表才是可选的。

CTE_query_definition

指定一个其结果集填充公用表表达式的 SELECT 语句。除了 CTE 不能定义另一个 CTE 以外，CTE_query_definition 的 SELECT 语句必须满足与创建视图时相同的要求。有关详细信息，请参阅“备注”部分和 CREATE VIEW (Transact-SQL)。

如果定义了多个 CTE_query_definition，则这些查询定义必须用下列一个集合运算符联接起来：UNION ALL、UNION、EXCEPT 或 INTERSECT。有关使用递归 CTE 查询定义的详细信息，请参阅下列“备注”部分和使用公用表表达式的递归查询。

示例

A. 创建一个简单公用表表达式

以下示例显示直接向 Adventure Works Cycles 的每个经理报告的雇员的数目。

	复制代码
USE AdventureWorks; GO WITH DirReps(ManagerID, DirectReports) AS ( SELECT ManagerID, COUNT(*) FROM HumanResources.Employee AS e WHERE ManagerID IS NOT NULL GROUP BY ManagerID ) SELECT ManagerID, DirectReports FROM DirReps ORDER BY ManagerID; GO

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USE AdventureWorks;
GO
WITH DirReps(ManagerID, DirectReports) AS 
(
    SELECT ManagerID, COUNT(*) 
    FROM HumanResources.Employee AS e
    WHERE ManagerID IS NOT NULL
    GROUP BY ManagerID
)
SELECT ManagerID, DirectReports 
FROM DirReps 
ORDER BY ManagerID;
GO

B. 使用公用表表达式来限制次数和报告平均数

以下示例显示向经理报告的雇员的平均数。

	复制代码
WITH DirReps (Manager, DirectReports) AS ( SELECT ManagerID, COUNT(*) AS DirectReports FROM HumanResources.Employee GROUP BY ManagerID ) SELECT AVG(DirectReports) AS [Average Number of Direct Reports] FROM DirReps WHERE DirectReports>= 2 ; GO

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WITH DirReps (Manager, DirectReports) AS 
(
    SELECT ManagerID, COUNT(*) AS DirectReports
    FROM HumanResources.Employee
    GROUP BY ManagerID
) 
SELECT AVG(DirectReports) AS [Average Number of Direct Reports]
FROM DirReps 
WHERE DirectReports>= 2 ;
GO

C. 多次引用同一个公用表表达式

以下示例显示 SalesOrderHeader 表中每个销售人员的销售订单的总数和最近的销售订单的日期。CTE 在运行的语句中被引用两次：一次返回为销售人员所选的列，另一次检索销售经理的类似详细信息。销售人员和销售经理的数据都返回在一行中。

	复制代码
USE AdventureWorks; GO WITH Sales_CTE (SalesPersonID, NumberOfOrders, MaxDate) AS ( SELECT SalesPersonID, COUNT(*), MAX(OrderDate) FROM Sales.SalesOrderHeader GROUP BY SalesPersonID ) SELECT E.EmployeeID, OS.NumberOfOrders, OS.MaxDate, E.ManagerID, OM.NumberOfOrders, OM.MaxDate FROM HumanResources.Employee AS E JOIN Sales_CTE AS OS ON E.EmployeeID = OS.SalesPersonID LEFT OUTER JOIN Sales_CTE AS OM ON E.ManagerID = OM.SalesPersonID ORDER BY E.EmployeeID; GO

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USE AdventureWorks;
GO
WITH Sales_CTE (SalesPersonID, NumberOfOrders, MaxDate)
AS
(
    SELECT SalesPersonID, COUNT(*), MAX(OrderDate)
    FROM Sales.SalesOrderHeader
    GROUP BY SalesPersonID
)
SELECT E.EmployeeID, OS.NumberOfOrders, OS.MaxDate,
    E.ManagerID, OM.NumberOfOrders, OM.MaxDate
FROM HumanResources.Employee AS E
    JOIN Sales_CTE AS OS
    ON E.EmployeeID = OS.SalesPersonID
    LEFT OUTER JOIN Sales_CTE AS OM
    ON E.ManagerID = OM.SalesPersonID
ORDER BY E.EmployeeID;
GO

使用递归公用表表达式显示递归的多个级别。

以下示例显示经理以及向经理报告的雇员的层次列表。

	复制代码
USE AdventureWorks; GO WITH DirectReports(ManagerID, EmployeeID, EmployeeLevel) AS ( SELECT ManagerID, EmployeeID, 0 AS EmployeeLevel FROM HumanResources.Employee WHERE ManagerID IS NULL UNION ALL SELECT e.ManagerID, e.EmployeeID, EmployeeLevel + 1 FROM HumanResources.Employee e INNER JOIN DirectReports d ON e.ManagerID = d.EmployeeID ) SELECT ManagerID, EmployeeID, EmployeeLevel FROM DirectReports ; GO

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USE AdventureWorks;
GO
WITH DirectReports(ManagerID, EmployeeID, EmployeeLevel) AS 
(
    SELECT ManagerID, EmployeeID, 0 AS EmployeeLevel
    FROM HumanResources.Employee
    WHERE ManagerID IS NULL
    UNION ALL
    SELECT e.ManagerID, e.EmployeeID, EmployeeLevel + 1
    FROM HumanResources.Employee e
        INNER JOIN DirectReports d
        ON e.ManagerID = d.EmployeeID 
)
SELECT ManagerID, EmployeeID, EmployeeLevel 
FROM DirectReports ;
GO

E. 使用递归公用表表达式显示递归的两个级别。

以下示例显示经理以及向经理报告的雇员。将返回的级别数目被限制为两个。

	复制代码
USE AdventureWorks; GO WITH DirectReports(ManagerID, EmployeeID, EmployeeLevel) AS ( SELECT ManagerID, EmployeeID, 0 AS EmployeeLevel FROM HumanResources.Employee WHERE ManagerID IS NULL UNION ALL SELECT e.ManagerID, e.EmployeeID, EmployeeLevel + 1 FROM HumanResources.Employee e INNER JOIN DirectReports d ON e.ManagerID = d.EmployeeID ) SELECT ManagerID, EmployeeID, EmployeeLevel FROM DirectReports WHERE EmployeeLevel <= 2 ; GO

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USE AdventureWorks;
GO
WITH DirectReports(ManagerID, EmployeeID, EmployeeLevel) AS 
(
    SELECT ManagerID, EmployeeID, 0 AS EmployeeLevel
    FROM HumanResources.Employee
    WHERE ManagerID IS NULL
    UNION ALL
    SELECT e.ManagerID, e.EmployeeID, EmployeeLevel + 1
    FROM HumanResources.Employee e
        INNER JOIN DirectReports d
        ON e.ManagerID = d.EmployeeID 
)
SELECT ManagerID, EmployeeID, EmployeeLevel 
FROM DirectReports 
WHERE EmployeeLevel <= 2 ;
GO

F. 使用递归公用表表达式显示层次列表

以下示例在示例 C 的基础上添加经理和雇员的名称，以及他们各自的头衔。通过缩进各个级别，突出显示经理和雇员的层次结构。

	复制代码
USE AdventureWorks; GO WITH DirectReports(Name, Title, EmployeeID, EmployeeLevel, Sort) AS (SELECT CONVERT(varchar(255), c.FirstName + ' ' + c.LastName), e.Title, e.EmployeeID, 1, CONVERT(varchar(255), c.FirstName + ' ' + c.LastName) FROM HumanResources.Employee AS e JOIN Person.Contact AS c ON e.ContactID = c.ContactID WHERE e.ManagerID IS NULL UNION ALL SELECT CONVERT(varchar(255), REPLICATE ('\| ' , EmployeeLevel) + c.FirstName + ' ' + c.LastName), e.Title, e.EmployeeID, EmployeeLevel + 1, CONVERT (varchar(255), RTRIM(Sort) + '\| ' + FirstName + ' ' + LastName) FROM HumanResources.Employee as e JOIN Person.Contact AS c ON e.ContactID = c.ContactID JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID ) SELECT EmployeeID, Name, Title, EmployeeLevel FROM DirectReports ORDER BY Sort; GO

复制代码

USE AdventureWorks;
GO
WITH DirectReports(Name, Title, EmployeeID, EmployeeLevel, Sort)
AS (SELECT CONVERT(varchar(255), c.FirstName + ' ' + c.LastName),
        e.Title,
        e.EmployeeID,
        1,
        CONVERT(varchar(255), c.FirstName + ' ' + c.LastName)
    FROM HumanResources.Employee AS e
    JOIN Person.Contact AS c ON e.ContactID = c.ContactID 
    WHERE e.ManagerID IS NULL
    UNION ALL
    SELECT CONVERT(varchar(255), REPLICATE ('| ' , EmployeeLevel) +
        c.FirstName + ' ' + c.LastName),
        e.Title,
        e.EmployeeID,
        EmployeeLevel + 1,
        CONVERT (varchar(255), RTRIM(Sort) + '| ' + FirstName + ' ' + 
                 LastName)
    FROM HumanResources.Employee as e
    JOIN Person.Contact AS c ON e.ContactID = c.ContactID
    JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID
    )
SELECT EmployeeID, Name, Title, EmployeeLevel
FROM DirectReports 
ORDER BY Sort;
GO

G. 使用 MAXRECURSION 取消一条语句

可以使用 MAXRECURSION 来防止不合理的递归 CTE 进入无限循环。以下示例有意创建了一个无限循环，然后使用 MAXRECURSION 提示来将递归级别限制为两个。

	复制代码
USE AdventureWorks; GO --Creates an infinite loop WITH cte (EmployeeID, ManagerID, Title) as ( SELECT EmployeeID, ManagerID, Title FROM HumanResources.Employee WHERE ManagerID IS NOT NULL UNION ALL SELECT cte.EmployeeID, cte.ManagerID, cte.Title FROM cte JOIN HumanResources.Employee AS e ON cte.ManagerID = e.EmployeeID ) --Uses MAXRECURSION to limit the recursive levels to 2 SELECT EmployeeID, ManagerID, Title FROM cte OPTION (MAXRECURSION 2); GO

复制代码

USE AdventureWorks;
GO
--Creates an infinite loop
WITH cte (EmployeeID, ManagerID, Title) as
(
    SELECT EmployeeID, ManagerID, Title
    FROM HumanResources.Employee
    WHERE ManagerID IS NOT NULL
  UNION ALL
    SELECT cte.EmployeeID, cte.ManagerID, cte.Title
    FROM cte 
    JOIN  HumanResources.Employee AS e 
        ON cte.ManagerID = e.EmployeeID
)
--Uses MAXRECURSION to limit the recursive levels to 2
SELECT EmployeeID, ManagerID, Title
FROM cte
OPTION (MAXRECURSION 2);
GO

在更正代码错误之后，就不再需要 MAXRECURSION。以下示例显示了更正后的代码。

	复制代码
USE AdventureWorks; GO WITH cte (EmployeeID, ManagerID, Title) AS ( SELECT EmployeeID, ManagerID, Title FROM HumanResources.Employee WHERE ManagerID IS NOT NULL UNION ALL SELECT e.EmployeeID, e.ManagerID, e.Title FROM HumanResources.Employee AS e JOIN cte ON e.ManagerID = cte.EmployeeID ) SELECT EmployeeID, ManagerID, Title FROM cte; GO

复制代码

USE AdventureWorks;
GO
WITH cte (EmployeeID, ManagerID, Title)
AS
(
    SELECT EmployeeID, ManagerID, Title
    FROM HumanResources.Employee
    WHERE ManagerID IS NOT NULL
  UNION ALL
    SELECT  e.EmployeeID, e.ManagerID, e.Title
    FROM HumanResources.Employee AS e
    JOIN cte ON e.ManagerID = cte.EmployeeID
)
SELECT EmployeeID, ManagerID, Title
FROM cte;
GO

H. 使用公用表表达式来有选择地执行 SELECT 语句中的递归操作

以下示例显示了为 ProductAssemblyID = 800 生产自行车所需的产品装配和部件层次结构。

	复制代码
USE AdventureWorks; GO WITH Parts(AssemblyID, ComponentID, PerAssemblyQty, EndDate, ComponentLevel) AS ( SELECT b.ProductAssemblyID, b.ComponentID, b.PerAssemblyQty, b.EndDate, 0 AS ComponentLevel FROM Production.BillOfMaterials AS b WHERE b.ProductAssemblyID = 800 AND b.EndDate IS NULL UNION ALL SELECT bom.ProductAssemblyID, bom.ComponentID, p.PerAssemblyQty, bom.EndDate, ComponentLevel + 1 FROM Production.BillOfMaterials AS bom INNER JOIN Parts AS p ON bom.ProductAssemblyID = p.ComponentID AND bom.EndDate IS NULL ) SELECT AssemblyID, ComponentID, Name, PerAssemblyQty, EndDate, ComponentLevel FROM Parts AS p INNER JOIN Production.Product AS pr ON p.ComponentID = pr.ProductID ORDER BY ComponentLevel, AssemblyID, ComponentID; GO

复制代码

USE AdventureWorks;
GO
WITH Parts(AssemblyID, ComponentID, PerAssemblyQty, EndDate, ComponentLevel) AS
(
    SELECT b.ProductAssemblyID, b.ComponentID, b.PerAssemblyQty,
        b.EndDate, 0 AS ComponentLevel
    FROM Production.BillOfMaterials AS b
    WHERE b.ProductAssemblyID = 800
          AND b.EndDate IS NULL
    UNION ALL
    SELECT bom.ProductAssemblyID, bom.ComponentID, p.PerAssemblyQty,
        bom.EndDate, ComponentLevel + 1
    FROM Production.BillOfMaterials AS bom 
        INNER JOIN Parts AS p
        ON bom.ProductAssemblyID = p.ComponentID
        AND bom.EndDate IS NULL
)
SELECT AssemblyID, ComponentID, Name, PerAssemblyQty, EndDate,
        ComponentLevel 
FROM Parts AS p
    INNER JOIN Production.Product AS pr
    ON p.ComponentID = pr.ProductID
ORDER BY ComponentLevel, AssemblyID, ComponentID;
GO

I. 在 UPDATE 语句中使用递归 CTE

以下示例将直接或间接向 ManagerID 12 报告的所有雇员的 VacationHours 值增加 25%。公用表表达式返回一个向 ManagerID 12 直接报告的雇员的层次列表，以及向这些雇员报告的雇员的层次列表，等等。只修改公用表表达式所返回的行。

	复制代码
USE AdventureWorks; GO WITH DirectReports(EmployeeID, NewVacationHours, EmployeeLevel) AS (SELECT e.EmployeeID, e.VacationHours, 1 FROM HumanResources.Employee AS e WHERE e.ManagerID = 12 UNION ALL SELECT e.EmployeeID, e.VacationHours, EmployeeLevel + 1 FROM HumanResources.Employee as e JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID ) UPDATE HumanResources.Employee SET VacationHours = VacationHours * 1.25 FROM HumanResources.Employee AS e JOIN DirectReports AS d ON e.EmployeeID = d.EmployeeID; GO

复制代码

USE AdventureWorks;
GO
WITH DirectReports(EmployeeID, NewVacationHours, EmployeeLevel)
AS
(SELECT e.EmployeeID, e.VacationHours, 1
  FROM HumanResources.Employee AS e
  WHERE e.ManagerID = 12
  UNION ALL
  SELECT e.EmployeeID, e.VacationHours, EmployeeLevel + 1
  FROM HumanResources.Employee as e
  JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID
)
UPDATE HumanResources.Employee
SET VacationHours = VacationHours * 1.25
FROM HumanResources.Employee AS e
JOIN DirectReports AS d ON e.EmployeeID = d.EmployeeID;
GO

使用多个定位点和递归成员

以下示例使用多个定位点和递归成员来返回指定的人的所有祖先。创建了一个表，并在表中插入值，以建立由递归 CTE 返回的宗谱。

	复制代码
-- Genealogy table IF OBJECT_ID('Person','U') IS NOT NULL DROP TABLE Person; GO CREATE TABLE Person(ID int, Name varchar(30), Mother int, Father int); GO INSERT Person VALUES(1, 'Sue', NULL, NULL); INSERT Person VALUES(2, 'Ed', NULL, NULL); INSERT Person VALUES(3, 'Emma', 1, 2); INSERT Person VALUES(4, 'Jack', 1, 2); INSERT Person VALUES(5, 'Jane', NULL, NULL); INSERT Person VALUES(6, 'Bonnie', 5, 4); INSERT Person VALUES(7, 'Bill', 5, 4); GO -- Create the recursive CTE to find all of Bonnie's ancestors. WITH Generation (ID) AS ( -- First anchor member returns Bonnie's mother. SELECT Mother FROM Person WHERE Name = 'Bonnie' UNION -- Second anchor member returns Bonnie's father. SELECT Father FROM Person WHERE Name = 'Bonnie' UNION ALL -- First recursive member returns male ancestors of the previous generation. SELECT Person.Father FROM Generation, Person WHERE Generation.ID=Person.ID UNION ALL -- Second recursive member returns female ancestors of the previous generation. SELECT Person.Mother FROM Generation, Person WHERE Generation.ID=Person.ID ) SELECT Person.ID, Person.Name, Person.Mother, Person.Father FROM Generation, Person WHERE Generation.ID = Person.ID; GO

复制代码

-- Genealogy table
IF OBJECT_ID('Person','U') IS NOT NULL DROP TABLE Person;
GO
CREATE TABLE Person(ID int, Name varchar(30), Mother int, Father int);
GO
INSERT Person VALUES(1, 'Sue', NULL, NULL);
INSERT Person VALUES(2, 'Ed', NULL, NULL);
INSERT Person VALUES(3, 'Emma', 1, 2);
INSERT Person VALUES(4, 'Jack', 1, 2);
INSERT Person VALUES(5, 'Jane', NULL, NULL);
INSERT Person VALUES(6, 'Bonnie', 5, 4);
INSERT Person VALUES(7, 'Bill', 5, 4);
GO
-- Create the recursive CTE to find all of Bonnie's ancestors.
WITH Generation (ID) AS
(
-- First anchor member returns Bonnie's mother.
    SELECT Mother 
    FROM Person
    WHERE Name = 'Bonnie'
UNION
-- Second anchor member returns Bonnie's father.
    SELECT Father 
    FROM Person
    WHERE Name = 'Bonnie'
UNION ALL
-- First recursive member returns male ancestors of the previous generation.
    SELECT Person.Father
    FROM Generation, Person
    WHERE Generation.ID=Person.ID
UNION ALL
-- Second recursive member returns female ancestors of the previous generation.
    SELECT Person.Mother
    FROM Generation, Person
    WHERE Generation.ID=Person.ID
)
SELECT Person.ID, Person.Name, Person.Mother, Person.Father
FROM Generation, Person
WHERE Generation.ID = Person.ID;
GO

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关于SQL语句中With的用法

创建和使用 CTE 的指南

定义和使用递归 CTE 指南

参数

示例

A. 创建一个简单公用表表达式

B. 使用公用表表达式来限制次数和报告平均数

C. 多次引用同一个公用表表达式

使用递归公用表表达式显示递归的多个级别。

E. 使用递归公用表表达式显示递归的两个级别。

F. 使用递归公用表表达式显示层次列表

G. 使用 MAXRECURSION 取消一条语句

H. 使用公用表表达式来有选择地执行 SELECT 语句中的递归操作

I. 在 UPDATE 语句中使用递归 CTE

使用多个定位点和递归成员

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