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附注：微软认证考试70-461范围
- Create Database Objects创建数据库对象 (24%)
- Work with Data数据处理 (27%)
- Modify Data数据修改 (24%)
- Troubleshoot & Optimize故障排解及SQL优化 (25%)
本文是第二节Work with Data 数据处理 。 第一部分直通车 第二部分直通车 第三部分直通车 第四部分直通车 第五部分：Query and manage XML data. May include but not limited to: understand xml datatypes and their schemas and interop w/, limitations & restrictions; implement XML schemas and handling of XML data; XML data: how to handle it in SQL Server and when and when not to use it, including XML namespaces; import and export xml; xml indexing. XML数据的查询与管理。可能包含但不仅限于：理解XML类型，架构，交互，局限性和约束性；实现XML架构和XML数据的处理；了解什么时候使用XML比较恰当，包括XML命名空间；导入导出XML；XML索引。 FOX XML指定EXPLICIT
FOR XML 模式可以是 RAW、AUTO、EXPLICIT 或 PATH。它确定产生的 XML 的形状。基本语法： [ FOR { BROWSE | <XML> } ]
<XML> ::=
XML
{
{ RAW [ ('ElementName') ] | AUTO }
[
<CommonDirectives>
[ , { XMLDATA | XMLSCHEMA [ ('TargetNameSpaceURI') ]} ]
[ , ELEMENTS [ XSINIL | ABSENT ]
| EXPLICIT
[
<CommonDirectives>
[ , XMLDATA ]
| PATH [ ('ElementName') ]
[
<CommonDirectives>
[ , ELEMENTS [ XSINIL | ABSENT ] ]
}
<CommonDirectives> ::=
[ , BINARY BASE64 ]
[ , TYPE ]
[ , ROOT [ ('RootName') ] ]
FOX XML指定EXPLICIT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 parentclothes!1!categorysubcategory!2!namesubsubcategory!3!name
1 NULL 衣服 NULL NULL
2 1 NULL 女装 NULL
3 2 NULL NULL 上衣
3 2 NULL NULL 裤子
执行FOR XML EXPLICIT结果(就是上述SQL后添加FOR XML EXPLICIT)： <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 。
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： tag parentclothes!1!categoryclothes!1!idsubcategory!2!namesubcategory!2!idsubsubcategory!3!namesubsubcategory!3!id
1 NULL 衣服 1111 NULL NULL NULL NULL
2 1 NULL NULL 女装 2222 NULL 0
3 2 NULL NULL NULL 0 上衣 3331
3 2 NULL NULL NULL 0 裤子 3332
运行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ELEMENTwith 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>
指定ELEMENTXSINILwith 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>
指定 ID 和 IDREF with TestXmlExplicit
as
(
select 1 as tag,null as parent,N'乐可乐可的部落格' 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="乐可乐可的部落格" 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 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 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>
指定CDATAwith 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XMLTEXTwith 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>
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