SQL SERVER中XML查询：FOR XML指定EXPLICIT

SQL SERVER中XML查询：FOR XML指定EXPLICIT

前言

在SQL SERVER中，XML查询可以指定RAW，AUTO，EXPLICIT，PATH。本文用一些实例介绍SQL SERVER中指定EXPLICIT的XML查询。

基础示例

一个简单的EXPLICIT例子：

with TestXmlExplicit
as
(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],null as [subcategory!2!name],null as [subsubcategory!3!name]
union all
select 2,1,null,'女装',null
union all
select 3,2,null,null,'上衣'
union all
select 3,2,null,null,'裤子'
)
select * from TestXmlExplicit

结果：

tag	parent	clothes!1!category	subcategory!2!name	subsubcategory!3!name
1		衣服
2	1		女装
3	2			上衣
3	2			裤子

注：上面空值项为null值，把它变成空白为了结果的清晰。

执行FOR XML EXPLICIT(就是上述SQL后添加FOR XML EXPLICIT)：

with TestXmlExplicit
as
(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],null as [subcategory!2!name],null as [subsubcategory!3!name]
union all
select 2,1,null,'女装',null
union all
select 3,2,null,null,'上衣'
union all
select 3,2,null,null,'裤子'
)
select * from TestXmlExplicit FOR XML EXPLICIT

结果：

<clothes category="衣服">

  <subcategory name="女装">

    <subsubcategory name="上衣" />

    <subsubcategory name="裤子" />

  </subcategory>

</clothes>

分析FOR XML EXPLICIT

TAG和PARENT列是必须的。PARENT为NULL或0的是根目录。列名上叹号间的数字对应TAG。

拿三级目录来说，在一级和二级目录对应列上设为NULL值即可，因为三级目灵只关心三级目录列就行了。如TAG为3的两行，clothes!1!category和subcategory!2!name没有对应值。

任意指定同级目录

TAG数字不代表目录级别！下面是新同级目录的例子：

with TestXmlExplicit

as

(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],null as [subcategory!2!name],null as [subsubcategory!3!name],null as [newcategoryname!4!name]
union all
select 2,1,null,'女装',null,null
union all
select 3,2,null,null,'上衣',null
union all
 
select 4,2,null,null,null,'裤子'

)

select * from TestXmlExplicit for xml explicit

结果：
<clothes category="衣服">

  <subcategory name="女装">

    <subsubcategory name="上衣" />

    <newcategoryname name="裤子" />
  </subcategory>
</clothes>

可以看出，三级目录中的元素名称已经更改成newcategoryname ，而”裤子“所在级别并不是四级目录。

为所有目录添加新属性

现在给每级目录添加属性ID，新SQL语句如下：

with TestXmlExplicit

as

(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],1111 as [clothes!1!id],null as [subcategory!2!name],null as [subcategory!2!id],null as [subsubcategory!3!name],null as [subsubcategory!3!id]
union all
select 2,1,null,null,'女装',2222,null,0
union all
select 3,2,null,null,null,0,'上衣',3331
union all
 
select 3,2,null,null,null,0,'裤子',3332

)

select * from TestXmlExplicit

结果：



注：上面空值项为null值，把它变成空白为了结果的清晰。

运行FOR XML EXPLICIT

with TestXmlExplicit
as
(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],1111 as [clothes!1!id],null as [subcategory!2!name],null as [subcategory!2!id],null as [subsubcategory!3!name],null as [subsubcategory!3!id]
union all
select 2,1,null,null,'女装',2222,null,0
union all
select 3,2,null,null,null,0,'上衣',3331
union all
select 3,2,null,null,null,0,'裤子',3332
)
select * from TestXmlExplicit FOR XML EXPLICIT

结果
<clothes category="衣服" id="1111">

  <subcategory name="女装" id="2222">

    <subsubcategory name="上衣" id="3331" />

    <subsubcategory name="裤子" id="3332" />

  </subcategory>

</clothes>

指定ELEMENT

with TestXmlExplicit

as

(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],1111 as [clothes!1!id],null as [subcategory!2!name],null as [subcategory!2!id],null as [subsubcategory!3!name!element],null
as [subsubcategory!3!id!element]
union all
select 2,1,null,null,'女装',2222,null,0
union all
select 3,2,null,null,null,0,'上衣',3331
union all
 
select 3,2,null,null,null,0,'裤子',3332

)

select * from TestXmlExplicit for xml explicit

红色字体部分指定了element，结果：

<clothes category="衣服" id="1111">

  <subcategory name="女装" id="2222">

    <subsubcategory>

      <name>上衣</name>

      <id>3331</id>

    </subsubcategory>

    <subsubcategory>

      <name>裤子</name>

      <id>3332</id>

    </subsubcategory>

  </subcategory>

</clothes>

需要注意的是，如果指定element的项为空值，结果集中将不显示该项，如：
with TestXmlExplicit
as
(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],1111
as [clothes!1!id],null as [subcategory!2!name],null as [subcategory!2!id],null as [subsubcategory!3!name!element],null
as [subsubcategory!3!id!element]
union all
select 2,1,null,null,'女装',2222,null,0
union all
select 3,2,null,null,null,0,'上衣',3331
union all 
select 3,2,null,null,null,0,'裤子',null
)
select * from TestXmlExplicit for xml explicit

结果：
<clothes category="衣服" id="1111">

  <subcategory name="女装" id="2222">

    <subsubcategory>

      <name>上衣</name>

      <id>3331</id>

    </subsubcategory>

    <subsubcategory>

      <name>裤子</name>

    </subsubcategory>

  </subcategory>

</clothes>

注意裤子下面的ID项不再存在，如果你想要显示具有空值的该项，需要指定elementxsinil。

指定ELEMENTXSINIL

with TestXmlExplicit

as

(
select 1 as tag,null as parent,'衣服' as [clothes!1!category],1111 as [clothes!1!id],null as [subcategory!2!name],null as [subcategory!2!id],null as [subsubcategory!3!name!element],null as [subsubcategory!3!id!ELEMENTXSINIL]
union all
select 2,1,null,null,'女装',2222,null,0
union all
select 3,2,null,null,null,0,'上衣',3331
union all
 
select 3,2,null,null,null,0,'裤子',null

)

select * from TestXmlExplicit for xml explicit

注意红色字体部分，最后一列指定了ELEMENTXSINIL，为了测试，把最后一行最后一列的值改为NULL。

结果：
<clothes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" category="衣服" id="1111">

  <subcategory name="女装" id="2222">

    <subsubcategory>

      <name>上衣</name>

      <id>3331</id>

    </subsubcategory>

    <subsubcategory>

      <name>裤子</name>

      <id xsi:nil="true" />
    </subsubcategory>
  </subcategory>
</clothes>

虽然裤子的id项是空值，但依然显示。

指定 ID 和 IDREF 

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'LeeWhoeeUniversity' as [clothes!1!category],'011' as [clothes!1!cloid!id],'099' as [clothes!1!cloidref!idref]

)

select * from TestXmlExplicit

结果：

tag	parent	clothes!1!category	clothes!1!cloid!id	clothes!1!cloidref!idref
1		LeeWhoeeUniversity	011	099

注：上面空值项为null值，把它变成空白为了结果的清晰。

执行for xml explicit,xmldata：

with TestXmlExplicit
as
(
select 1 as tag,null as parent,N'LeeWhoeeUniversity' as [clothes!1!category],'011'
as [clothes!1!cloid!id],'099' as [clothes!1!cloidref!idref]

)
select * from TestXmlExplicit for xml explicit,xmldata

红色字体为XML指定了ID和IDREF类型，通XMLDATA查看架构可知：

<Schema name="Schema6" xmlns="urn:schemas-microsoft-com:xml-data" xmlns:dt="urn:schemas-microsoft-com:datatypes">

  <ElementType name="clothes" content="mixed" model="open">

    <AttributeType name="category" dt:type="string" />

    <AttributeType name="cloid" dt:type="id" />

    <AttributeType name="cloidref" dt:type="idref" />

    <attribute type="category" />

    <attribute type="cloid" />

    <attribute type="cloidref" />

  </ElementType>

</Schema>

<clothes xmlns="x-schema:#Schema6" category="LeeWhoeeUniversity" cloid="011" cloidref="099" />

指定 IDREFS 指令

with TestXmlExplicit

as

(
select 1 as tag,0 as parent,null as [clothes!1!cloidlist!idrefs]
union all
select 1,0,'022'
union all
select 1,0,'025'

)

select * from TestXmlExplicit

结果集：

tag	parent	clothes!1!cloidlist!idrefs
1	0
1	0	022
1	0	025

注：上面空值项为null值，把它变成空白为了结果的清晰。

执行 for xml explicit,xmldata：

with TestXmlExplicit
as
(
select 1 as tag,0 as parent,null as [clothes!1!cloidlist!idrefs]
union all
select 1,0,'022'
union all
select 1,0,'025'

)
select * from TestXmlExplicit for xml explicit,xmldata

结果：
<Schema name="Schema4" xmlns="urn:schemas-microsoft-com:xml-data" xmlns:dt="urn:schemas-microsoft-com:datatypes">

  <ElementType name="clothes" content="mixed" model="open">

    <AttributeType name="cloidlist" dt:type="idrefs" />

    <attribute type="cloidlist" />

  </ElementType>

</Schema>

<clothes xmlns="x-schema:#Schema4" cloidlist="022 025"></clothes>

示例中cloidlist的类型是idrefs。IDREFS类型的元素也有多个值。因此，必须使用单独的 SELECT 子句来重复使用相同的标记、父级和键列信息。然后，ORDER
BY 必须确保组成IDREFS 值的行的序列成组显示在它们的父元素下。

指定 HIDE 

HIDE顾名思义，隐藏信息。

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!name],null as [subsubcategory!3!name!hide]
union all
select 2,1,null,N'女装',null
union all
select 3,2,null,null,N'上衣'
union all
 
select 3,2,null,null,N'裤子'

)

select * from TestXmlExplicit

结果：

tag	parent	clothes!1!category	subcategory!2!name	subsubcategory!3!name!hide
1		衣服
2	1		女装
3	2			上衣
3	2			裤子

注：上面空值项为null值，把它变成空白为了结果的清晰。

执行for xml explicit：

with TestXmlExplicit
as
(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null
as [subcategory!2!name],null as [subsubcategory!3!name!hide]
union all
select 2,1,null,N'女装',null
union all
select 3,2,null,null,N'上衣'
union all 
select 3,2,null,null,N'裤子'
)
select * from TestXmlExplicit for xml explicit

三级目录的subsubcategory!3!name不会显示在结果中，但是HIDE的列可以用来排序。

结果：
<clothes category="衣服">

  <subcategory name="女装">

    <subsubcategory />

    <subsubcategory />

  </subcategory>

</clothes>

指定ELEMENT和XML的不同

指定ELEMENT会实体化数据即对特殊字符进行转义，XML则不会。

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!name!element],null as [subcategory!2!name2!xml]
union all
select 2,1,null,N'<b>女装</b>',N'<b>男装</b>'

)

select * from TestXmlExplicit for xml explicit

结果:
<clothes category="衣服">

  <subcategory>

    <name><b>女装</b></name>

    <name2>

      <b>男装</b>

    </name2>

  </subcategory>

</clothes>

上面可以看到女装部分被转义，男装部分没有。

指定CDATA

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!name!cdata]
union all
select 2,1,null,N'<b>女装</b>'

)

select * from TestXmlExplicit for xml explicit

结果：
<clothes category="衣服">

  <subcategory>

    <name><![CDATA[<b>女装</b>]]></name>

  </subcategory>

</clothes>

指定XMLTEXT

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!NAME],null as [subcategory!2!!XMLTEXT]
union all
select 2,1,null,N'女装',N'<s NAME="test" id="12">女装补充</s>'

)

select * from TestXmlExplicit for xml explicit

结果：

<clothes category="衣服">

  <subcategory NAME="女装" id="12">女装补充</subcategory>

</clothes>

因为对于红色字体 列没有指定 AttributeName，而指定了xmltext 指令，所以 <s>元素中的属性被追加到包含它的 <subcategory> 元素(即subcategory!2!NAME，不是clothes!1!category)的属性列表中。

因为 <xmltext> 元素中的 NAME属性与相同元素级上检索到的 NAME 属性冲突，所以忽略 <xmltext> 元素中的此属性，即使 NAME 为 NULL 也是如此。通常情况下，属性将覆盖溢出中具有相同名称的属性。但是id属性没有冲突，所以保留。

再看另一种情况：

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!NAME],null as [subcategory!2!!XMLTEXT]
union all
select 2,1,null,N'女装',N'<s NAME="test" id="12"><name>子元素</name></s>'

)

select * from TestXmlExplicit for xml explicit

XMLTEXT列值包含了子元素name, 因此当前元素追加到<subcategory>，<name>子元素</name>则作为子元素追加到<subcategory>，结果：
<clothes category="衣服">

  <subcategory NAME="女装" id="12">

    <name>子元素</name>

  </subcategory>

</clothes>

再看：

with TestXmlExplicit

as

(
select 1 as tag,null as parent,N'衣服' as [clothes!1!category],null as [subcategory!2!NAME],null as [subcategory!2!subname!XMLTEXT]
union all
select 2,1,null,N'女装',N'<s NAME="test" id="12"><name>子元素</name></s>'

)

select * from TestXmlExplicit for xml explicit

如果为XMLTEXT指定AttributeName(如subname)，则<s>的属性追加到<subname>，然后作为子元素追加到<subcategory>，结果：

<clothes category="衣服">

  <subcategory NAME="女装">

    <subname NAME="test" id="12">

      <name>子元素</name>

    </subname>

  </subcategory>

</clothes>

总结

以上对指定EXPLICIT的XML查询就介绍完了，下一篇文章将继续用实例介绍SQL SERVER中的XML查询：指定PATH查询。

SQL SERVER中XML查询：FOR XML指定RAW
SQL SERVER中XML查询：FOR XML指定AUTO

SQL SERVER中XML查询：FOR XML指定EXPLICIT

SQL SERVER中XML查询：FOR XML指定PATH
关于XML类型，请参考：http://blog.csdn.net/leewhoee/article/details/8571286
关于XML索引，请参考：http://blog.csdn.net/leewhoee/article/details/8579743

SQL SERVER中XML查询：FOR XML指定EXPLICIT

SQL SERVER中XML查询：FOR XML指定PATH