SQL中FOR XML子句的各种用法

FOR XML子句有四种最基本的模式，如上图所示：

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<Row>元素，每一列的值作为<Row>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

 

具体实例如下：

1、AUTO模式

(1). SQL语句：

   1:  SELECT EmployeeID,FirstName,LastName FROM Employees FOR XML AUTO, XMLSCHEMA

(2). 所生成的XML文件：

返回XML文件的XML Schema

<xsd:schema targetNamespace="urn:schemas-microsoft-com:sql:SqlRowSet1" xmlns:schema="urn:schemas-microsoft-com:sql:SqlRowSet1" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:sqltypes="http://schemas.microsoft.com/sqlserver/2004/sqltypes" elementFormDefault="qualified">
  <xsd:import namespace="http://schemas.microsoft.com/sqlserver/2004/sqltypes" schemaLocation="http://schemas.microsoft.com/sqlserver/2004/sqltypes/sqltypes.xsd" />
  <xsd:element name="Employees">
    <xsd:complexType>
      <xsd:attribute name="EmployeeID" type="sqltypes:int" use="required" />
      <xsd:attribute name="FirstName" use="required">
        <xsd:simpleType>
          <xsd:restriction base="sqltypes:nvarchar" sqltypes:localeId="1033" sqltypes:sqlCompareOptions="IgnoreCase IgnoreKanaType IgnoreWidth" sqltypes:sqlSortId="52">
            <xsd:maxLength value="10" />
          </xsd:restriction>
        </xsd:simpleType>
      </xsd:attribute>
      <xsd:attribute name="LastName" use="required">
        <xsd:simpleType>
          <xsd:restriction base="sqltypes:nvarchar" sqltypes:localeId="1033" sqltypes:sqlCompareOptions="IgnoreCase IgnoreKanaType IgnoreWidth" sqltypes:sqlSortId="52">
            <xsd:maxLength value="20" />
          </xsd:restriction>
        </xsd:simpleType>
      </xsd:attribute>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="1" FirstName="Nancy" LastName="Davolio" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="2" FirstName="Andrew" LastName="Fuller" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="3" FirstName="Janet" LastName="Leverling" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="4" FirstName="Margaret" LastName="Peacock" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="5" FirstName="Steven" LastName="Buchanan" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="6" FirstName="Michael" LastName="Suyama" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="7" FirstName="Robert" LastName="King" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="8" FirstName="Laura" LastName="Callahan" />
<Employees xmlns="urn:schemas-microsoft-com:sql:SqlRowSet1" EmployeeID="9" FirstName="Anne" LastName="Dodsworth" />

2、RAW模式

(1). SQL语句：

   1:  ----将元素命名为自定义的名称Employee

   2:  SELECT EmployeeID,FirstName,LastName FROM Employees FOR XML RAW ('Employee')

(2). 所生成的XML文件：

   1:  <Employee EmployeeID="1" FirstName="Nancy" LastName="Davolio" />

   2:  <Employee EmployeeID="2" FirstName="Andrew" LastName="Fuller" />

   3:  <Employee EmployeeID="3" FirstName="Janet" LastName="Leverling" />

   4:  <Employee EmployeeID="4" FirstName="Margaret" LastName="Peacock" />

   5:  <Employee EmployeeID="5" FirstName="Steven" LastName="Buchanan" />

   6:  <Employee EmployeeID="6" FirstName="Michael" LastName="Suyama" />

   7:  <Employee EmployeeID="7" FirstName="Robert" LastName="King" />

   8:  <Employee EmployeeID="8" FirstName="Laura" LastName="Callahan" />

   9:  <Employee EmployeeID="9" FirstName="Anne" LastName="Dodsworth" />

3、PATH模式：

(1). SQL语句：

SELECT EmployeeID "@ID",FirstName  "Name/FirstName",LastName "Name/LastName"

FROM Employees FOR XML PATH ('Employee')

(2). 所生成的XML文件

<Employee ID="1">
  <Name>
    <FirstName>Nancy</FirstName>
    <LastName>Davolio</LastName>
  </Name>
</Employee>
<Employee ID="2">
  <Name>
    <FirstName>Andrew</FirstName>
    <LastName>Fuller</LastName>
  </Name>
</Employee>
<Employee ID="3">
  <Name>
    <FirstName>Janet</FirstName>
    <LastName>Leverling</LastName>
  </Name>
</Employee>
<Employee ID="4">
  <Name>
    <FirstName>Margaret</FirstName>
    <LastName>Peacock</LastName>
  </Name>
</Employee>
<Employee ID="5">
  <Name>
    <FirstName>Steven</FirstName>
    <LastName>Buchanan</LastName>
  </Name>
</Employee>
<Employee ID="6">
  <Name>
    <FirstName>Michael</FirstName>
    <LastName>Suyama</LastName>
  </Name>
</Employee>
<Employee ID="7">
  <Name>
    <FirstName>Robert</FirstName>
    <LastName>King</LastName>
  </Name>
</Employee>
<Employee ID="8">
  <Name>
    <FirstName>Laura</FirstName>
    <LastName>Callahan</LastName>
  </Name>
</Employee>

4、EXPLICIT模式

问题：加入要生成如下的XML文档该如何操作？

<Employee EmpID="1">

<FirstName>Nancy</FirstName>

<LastName>Davolio</LastName>

</Employee>

EXPLICIT模式解决这个问题的应用分为两个主要步骤：

1.定义要输出的XML文档结构；

2.传入实际的数据值；

(1). SQL语句：

--定义输出XML文档的数据结构

SELECT  1 AS Tag,

        NULL AS Parent,

        EmployeeID AS [Employee!1!EmpID],

        FirstName AS [Employee!1!FirstName!element],

        LastName AS [Employee!1!LastName!element]

FROM    Employees

UNION ALL

--传入实际的数据

SELECT  1,

        NULL,

        EmployeeID,

        FirstName,

        LastName

FROM    Employees

ORDER BY [Employee!1!EmpID],

        [Employee!1!FirstName!element],

        [Employee!1!LastName!element]

FOR     XML EXPLICIT

语句含义的解释：

先看看定义XML结构的语句输出结果：

Tag栏用来指定生成元素的嵌套水平；1表示嵌套水平为

Parent栏用来指定当前Tag的父级层次；Null值表示该元素为顶级元素；

EmployeeID AS [Employee!1!EmpID],

说明：当前元素或属性的父级元素的名称！元素的标签号！元素或属性的名称
FirstName AS [Employee!1!FirstName!element],

说明：当前元素或属性的父级元素的名称！元素的标签号！元素或属性的名称！指定值作为元素输出

5、为输出的XML文档添加根元素(Root element)

(1). SQL语句：

SELECT EmployeeID,FirstName,LastName FROM Employees FOR XML AUTO, ROOT('MyRoot')

(2). 所生成的XML文件

<MyRoot>
  <Employees EmployeeID="1" FirstName="Nancy" LastName="Davolio" />
  <Employees EmployeeID="2" FirstName="Andrew" LastName="Fuller" />
  <Employees EmployeeID="3" FirstName="Janet" LastName="Leverling" />
  <Employees EmployeeID="4" FirstName="Margaret" LastName="Peacock" />
  <Employees EmployeeID="5" FirstName="Steven" LastName="Buchanan" />
  <Employees EmployeeID="6" FirstName="Michael" LastName="Suyama" />
  <Employees EmployeeID="7" FirstName="Robert" LastName="King" />
  <Employees EmployeeID="8" FirstName="Laura" LastName="Callahan" />
  <Employees EmployeeID="9" FirstName="Anne" LastName="Dodsworth" />
</MyRoot>