[2005每日一学]APPLY运算符（4）

SQLServer_2005 2006-08-02 01:09:46

使用 APPLY 运算符可以为实现查询操作的外部表表达式返回的每个行调用表值函数。表值函数作为右输入，外部表表达式作为左输入。通过对右输入求值来获得左输入每一行的计算结果，生成的行被组合起来作为最终输出。APPLY 运算符生成的列的列表是左输入中的列集，后跟右输入返回的列的列表。

APPLY 有两种形式： CROSS APPLY 和 OUTER APPLY。CROSS APPLY 仅返回外部表中通过表值函数生成结果集的行。OUTER APPLY 既返回生成结果集的行，也返回不生成结果集的行，其中表值函数生成的列中的值为 NULL。

示例：

--Create Employees table and insert values
CREATE TABLE Employees
(
empid int NOT NULL,
mgrid int NULL,
empname varchar(25) NOT NULL,
salary money NOT NULL,
CONSTRAINT PK_Employees PRIMARY KEY(empid),
)
GO
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 values
CREATE TABLE Departments
(
deptid INT NOT NULL PRIMARY KEY,
deptname VARCHAR(25) NOT NULL,
deptmgrid INT NULL REFERENCES Employees
)
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)

Departments 表中的大多数部门都有一个管理器 ID，该管理器 ID 与 Employees 表中的雇员相对应。下面的表值函数使用雇员 ID 作为参数，并返回该雇员及他/她的所有下属

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
(
-- Anchor Member (AM)
SELECT empid, empname, mgrid, 0
FROM employees
WHERE empid = @empid

UNION all

-- Recursive Member (RM)
SELECT e.empid, e.empname, e.mgrid, es.lvl+1
FROM employees AS e
JOIN employees_subtree AS es
ON e.mgrid = es.empid
)
INSERT INTO @TREE
SELECT * FROM Employees_Subtree

RETURN
END
GO

其中，上面的函数用到了CTE递归查询，相关的内容，可参考“Books Online"

若要返回每个部门经理的所有级别的全部下属，请使用下面的查询：

SELECT *
FROM Departments AS D
CROSS APPLY fn_getsubtree(D.deptmgrid) AS ST

查询结果如下：

1 HR 2 2 Andrew 1 0
1 HR 2 5 Steven 2 1
1 HR 2 6 Michael 2 1
2 Marketing 7 7 Robert 3 0
2 Marketing 7 11 David 7 1
2 Marketing 7 12 Ron 7 1
2 Marketing 7 13 Dan 7 1
2 Marketing 7 14 James 11 2
3 Finance 8 8 Laura 3 0
4 R&D 9 9 Ann 3 0
5 Training 4 4 Margaret 1 0
5 Training 4 10 Ina 4 1

修改查询为OUTER APPLY，结果为：
1 HR 2 2 Andrew 1 0
1 HR 2 5 Steven 2 1
1 HR 2 6 Michael 2 1
2 Marketing 7 7 Robert 3 0
2 Marketing 7 11 David 7 1
2 Marketing 7 12 Ron 7 1
2 Marketing 7 13 Dan 7 1
2 Marketing 7 14 James 11 2
3 Finance 8 8 Laura 3 0
4 R&D 9 9 Ann 3 0
5 Training 4 4 Margaret 1 0
5 Training 4 10 Ina 4 1
6 Gardening NULL NULL NULL NULL NULL

更多详细资料参考“Books Online"

以往帖子：
[2005每日一学]DDL触发器（1）
http://community.csdn.net/Expert/topic/4910/4910909.xml?temp=.5234644
2005每日一学]XML数据类型（2）
http://community.csdn.net/Expert/topic/4913/4913373.xml?temp=.579159
2005每日一学]排名函数（3）
http://community.csdn.net/Expert/topic/4918/4918884.xml?temp=.3263056

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