Question

目标：使用SQL Server 2012，尽可能简化xml检索。作为起点，指定默认根路径以及默认命名空间。

详细信息：

这两个表非常大，因此需要使用索引进行连接。我一直无法找到涵盖这种情况的示例，虽然我在使用FOR XML PATH构建xml表时看到类似的东西，类型，Root =

SqlFiddle：http://sqlfiddle.com/#!6/68df2/2/0

Create Table t1 (id int, MoreFields varchar(10), DateAdded datetime)
create Table t2 (id int, data xml)

--objective: Using the sql select structure below, make the default root path= /Doc/DocumentProperties

insert into t1 
values (1, 'other data', '2015-10-30 19:30:21.953'),
       (2, 'more data', '2015-10-30 19:30:21.953') 
insert into t2 
values (1,'<Doc xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.MyUrl.com" documentType="customDocument">
  <DocumentProperties>
    <DocumentID>1</DocumentID>
    <Title>blah blah</Title>
    <DateAdded>2015-10-30T15:30:21.9538615-04:00</DateAdded>
    <VisitID>123456</VisitID>
    <Patient>
      <ID>9876</ID>
      <FirstName>john</FirstName>
      <LastName>doe</LastName>
      <MiddleName />
    </Patient>
  </DocumentProperties>
</Doc>')            

;with XMLNamespaces (DEFAULT 'http://www.MyUrl.com')           
select 
    t1.id
    ,t1.DateAdded
    ,xmlDateAdded=t2.data.value('(/Doc/DocumentProperties/DateAdded)[1]', 'datetime') 
    ,Objective='Make /Doc/DocumentProperties the default root path, simplify node value retrieval'
    --since everything is under DocumentProperties I want to do something like: 
    --,xmlDateAdded2    =t2.DateAdded   or
    --,xmlDateAdded3    =?.value('/DateAdded','datetime')

    --will be retrieving other node values as well.
from t1 
inner join t2 
    on t1.id=t2.id 
where t1.id=1--in real world criteria is multiple rows

drop table t1
drop table t2

Answer 1

如果我正确理解了这个问题，你可以在CROSS APPLY上/Doc/DocumentProperties使其成为列XPath表达式的上下文，例如：

;with XMLNamespaces (DEFAULT 'http://www.MyUrl.com')           
select 
    t1.id
    ,t1.DateAdded
    ,xmlDateAdded=d.value('DateAdded[1]', 'datetime') 
from t1 
inner join t2 on t1.id=t2.id 
cross apply t2.data.nodes('/Doc/DocumentProperties') as x(d)
where t1.id=1

<强> Sqlfiddle Demo

请注意，在上面的示例中，您只需在XPath列中执行DateAdded[1]而不是更长的(/Doc/DocumentProperties/DateAdded)[1]。

T-SQL：xml如何使用内连接添加默认命名空间和根路径

1 个答案: