SQL Server递归实例

例子一

-- =============================================
-- 根据EID返回其下属的EID,Layer=1表示直接下属,NULL返回所有下属
-- select EID FROM F_Team_GetSubordinate(2,NULL)
-- =============================================
CREATE FUNCTION F_Team_GetSubordinate(
@EID INT,
@Layer INT)
RETURNS @tb TABLE (EID INT,NameCN varchar(50),SupervisorEID INT,Layer INT)
AS
BEGIN

;WITH CTE AS
(
SELECT EID,NameCn,SupervisorEID,0 as Layer FROM TCFG_Employee WHERE EID=@EID
UNION ALL
SELECT A.EID,A.NameCn,A.SupervisorEID,Layer=layer+1 FROM TCFG_Employee A
JOIN CTE B ON A.SupervisorEID = B.EID
)

INSERT INTO @tb
select EID,NameCN,SupervisorEID,Layer from CTE where (@Layer IS NULL OR Layer=@Layer)

return
END

GO

例子二

--[员工]表含成层级关系
CREATE TABLE Employees (
    empid INT NOT NULL,
    mgrid INT NULL,--管理者ID字段,用于链接empid
    empname VARCHAR (25) NOT NULL,
    salary money NOT NULL,
    CONSTRAINT PK_Employees PRIMARY KEY (empid),
)
GO

-- 插入实例数据,允许员工的管理者ID字段为null,
INSERT INTO Employees VALUES(1, NULL, 'Nancy', $10000.00)
INSERT INTO Employees VALUES(2, 1, 'Andrew', $5000.00)
INSERT INTO Employees VALUES(3, 1, 'Janet', $5000.00)
INSERT INTO Employees VALUES(4, 1, 'Margaret',$5000.00)
INSERT INTO Employees VALUES(5, 2, 'Steven', $2500.00)
INSERT INTO Employees VALUES(6, 2, 'Michael', $2500.00)
INSERT INTO Employees VALUES(7, 3, 'Robert', $2500.00)
INSERT INTO Employees VALUES(8, 3, 'Laura', $2500.00)
INSERT INTO Employees VALUES(9, 3, 'Ann', $2500.00)
INSERT INTO Employees VALUES(10, 4, 'Ina', $2500.00)
INSERT INTO Employees VALUES(11, 7, 'David', $2000.00)
INSERT INTO Employees VALUES(12, 7, 'Ron', $2000.00)
INSERT INTO Employees VALUES(13, 7, 'Dan', $2000.00)
INSERT INTO Employees VALUES(14, 11, 'James', $1500.00)
GO

--Create Departments table and insert demo values
CREATE TABLE Departments (
    deptid INT NOT NULL PRIMARY KEY,
    deptname VARCHAR (25) NOT NULL,
    deptmgrid INT NULL REFERENCES Employees --部门管理者ID,外键参考Employees的empid字段
)
GO

INSERT INTO Departments VALUES (1, 'HR', 2)
INSERT INTO Departments VALUES (2, 'Marketing', 7)
INSERT INTO Departments VALUES (3, 'Finance', 8)
INSERT INTO Departments VALUES (4, 'R&D', 9)
INSERT INTO Departments VALUES (5, 'Training', 4)
INSERT INTO Departments VALUES (6, 'Gardening', NULL)
GO
-- 这个自定义函数根据用工ID,返回他所有的下属(包括下属的下属,即所有层)
CREATE FUNCTION dbo.fn_getsubtree(@empid AS INT) RETURNS @TREE TABLE
(
  empid   INT NOT NULL,
  empname VARCHAR(25) NOT NULL,
  mgrid   INT NULL,
  lvl     INT NOT NULL
)
AS
BEGIN
  WITH Employees_Subtree(empid, empname, mgrid, lvl) AS  --lvl层级字段
  (
    -- Anchor Member (AM)
    SELECT empid, empname, mgrid, 0
    FROM employees
    WHERE empid = @empid  --这个查询输出将作为下个查询的输入!
        -- 下属,即那些管理者字段的值等于自己的Employee字段
    UNION all
    -- Recursive Member (RM)
    SELECT e.empid, e.empname, e.mgrid, es.lvl+1
    FROM employees AS e
    JOIN employees_subtree AS es --employees_subtree是WITH后面的变量名,相当于JOIN自己链接自己
    ON e.mgrid = es.empid
  )
  INSERT INTO @TREE
  SELECT * FROM Employees_Subtree
  RETURN
END
GO

-- Call for show
SELECT * FROM fn_getsubtree(1)

--通过这个例子理解CROSS APPLY 说明:表Departments和自定义函数fn_getsubtree链接
--查询每个部门管理者他们包含(所有层次)的下属,特别说明,返回的结果集的记录存在部分记录字段重复
--因为fn_getsubtree是返回所有层次的下属,所以下面的查询也返回每个部门下所有层次的下属
SELECT *
FROM Departments AS D
CROSS APPLY fn_getsubtree(D.deptmgrid) AS ST --deptmgrid 部门的领导id

例子三

WITH T AS
(
 SELECT empid, empname, mgrid,0 AS Lv FROM Employees
 UNION ALL
 SELECT e.empid, e.empname, e.mgrid,es.Lv+1 FROM Employees AS e --不支持*号!字段名必须一一写出来,并且和上面的SELECT一模一样!
 JOIN T AS es  --链接自己啊
 ON e.mgrid = es.empid
)
SELECT * FROM T

已经在好多场合看到这些的写法了,所有觉得比较重要.
===========================
用例数表
CREATE TABLE Employees (
 empid INT NOT NULL,
 mgrid INT NULL,--管理者字段,是自链接字段!
 empname VARCHAR (25) NOT NULL,
 salary money NOT NULL,
 CONSTRAINT PK_Employees PRIMARY KEY (empid),
)
GO

-- 允许员工的部门为null,
INSERT INTO Employees VALUES(1, NULL, 'Nancy', $10000.00)
INSERT INTO Employees VALUES(2, 1, 'Andrew', $5000.00)
INSERT INTO Employees VALUES(3, 1, 'Janet', $5000.00)
INSERT INTO Employees VALUES(4, 1, 'Margaret',$5000.00)
INSERT INTO Employees VALUES(5, 2, 'Steven', $2500.00)
INSERT INTO Employees VALUES(6, 2, 'Michael', $2500.00)
INSERT INTO Employees VALUES(7, 3, 'Robert', $2500.00)
INSERT INTO Employees VALUES(8, 3, 'Laura', $2500.00)
INSERT INTO Employees VALUES(9, 3, 'Ann', $2500.00)
INSERT INTO Employees VALUES(10, 4, 'Ina', $2500.00)
INSERT INTO Employees VALUES(11, 7, 'David', $2000.00)
INSERT INTO Employees VALUES(12, 7, 'Ron', $2000.00)
INSERT INTO Employees VALUES(13, 7, 'Dan', $2000.00)
INSERT INTO Employees VALUES(14, 11, 'James', $1500.00)
GO
=========================