SQL FOR XML子句的各种用法

FOR XML子句有四种最基本的模式
1、AUTO模式：返回数据表为起表名的元素，每一列的值返回为属性；
2、RAW模式：返回数据行为元素，每一列的值作为元素的属性；
3、PATH模式：通过简单的XPath语法来允许用户自定义嵌套的XML结构、元素、属性值
4、EXPLICIT模式：通过SELECT语法定义输出XML的结构
第1步：构造测试数据表及填充数据：
--1.建表语句
CREATE TABLE [dbo].[Users](
[UserID] [int] IDENTITY(1,1) NOT NULL,
[FirstName] [nvarchar](50) NULL,
[LastName] [nvarchar](50) NULL
)
--2.产生随机数SQL函数

CREATE FUNCTION [GenerateRandomItem] ( @LENGTH INT )
RETURNS NVARCHAR(255)
AS 
    BEGIN  
	--申明变量
        DECLARE @RandomNumber NVARCHAR(255)
        DECLARE @I SMALLINT
        DECLARE @RandNumber FLOAT
        DECLARE @Position TINYINT
        DECLARE @ExtractedCharacter VARCHAR(1)
        DECLARE @ValidCharacters VARCHAR(255)
        DECLARE @VCLength INT    
    --给变量赋值
        SET @ValidCharacters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'    
        SET @VCLength = LEN(@ValidCharacters)
        SET @ExtractedCharacter = ''
        SET @RandNumber = 0
        SET @Position = 0
        SET @RandomNumber = '' 
        
        SET @I = 1 
        WHILE @I < ( @Length + 1 ) 
            BEGIN 
                SET @RandNumber = (SELECT RandNumber FROM [RandNumberView])
                SET @Position = CONVERT(TINYINT, ( ( @VCLength - 1 )* @RandNumber + 1 ))
                SELECT  @ExtractedCharacter = SUBSTRING(@ValidCharacters,@Position, 1)
                SET @I = @I + 1
                SET @RandomNumber = @RandomNumber + @ExtractedCharacter
            END
        RETURN @RandomNumber
    END
GO
CREATE VIEW [RandNumberView]
AS  
SELECT  RAND() AS [RandNumber]

--3.添加测试数据

INSERT INTO Users  
        (   
          FirstName ,  
          LastName   
        )  
SELECT  
dbo.GenerateRandomItem(10),  
dbo.GenerateRandomItem(10)     
GO 10

--4.测试查询