递归查询

oracle
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Start with...Connect By子句递归查询一般用于一个表维护树形结构的应用。

创建示例表：

CREATE TABLE TBL_TEST
(
  ID    NUMBER,
  NAME  VARCHAR2(100 BYTE),
  PID   NUMBER                                  DEFAULT 0
);

 

插入测试数据：

INSERT INTO TBL_TEST(ID,NAME,PID) VALUES(''''1'''',''''10'''',''''0'''');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES(''''2'''',''''11'''',''''1'''');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES(''''3'''',''''20'''',''''0'''');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES(''''4'''',''''12'''',''''1'''');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES(''''5'''',''''121'''',''''2'''');

 

从Root往树末梢递归

select * from TBL_TEST
 start with id=1
 connect by prior id = pid

 

从末梢往树ROOT递归

select * from TBL_TEST
 start with id=5
 connect by prior pid = id

MSSQL
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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

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

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