在 T-SQL 中查询之前将字符串转换为 XML 数据类型

问题描述

如何将字符串转换为 XML 数据类型，以便我可以将数据作为 XML 查询:

How do I convert a string into an XML datatype so that I can query the data as XML:

例如(感谢mellamokb the Wise"为此提供了原始 SQL)

For example (thanks to "mellamokb the Wise" who provided the original SQL for this)

如果 xmlstring 是 XML 类型，则下面的代码可以正常工作(请参阅 DEMO)

The code below works fine if xmlstring is of the type XML (see DEMO)

select id, name
from Data
cross apply (
  select Destination.value('data(@Name)', 'varchar(50)') as name
  from [xmlstring].nodes('/Holidays/Summer/Regions/Destinations/Destination') D(Destination)
) Destinations(Name)

但是，如果 xmlString 是 varchar 类型，即使我将字符串转换为 XML，我也会收到错误消息 (演示):

However, if xmlString is of type varchar I get an error even though I'm converting the string to XML (DEMO):

select id, name
from Data
  cross apply (
  select Destination.value('data(@Name)', 'varchar(50)') as name
  from CONVERT(xml,[xmlstring]).nodes('/Holidays/Summer/Regions/Destinations/Destination') D(Destination)
) Destinations(Name)

推荐答案

您可以在一个额外的交叉应用中进行转换.

You can do the cast it in one extra cross apply.

select id,
       T.N.value('@Name', 'varchar(50)') as name
from Data
cross apply (select cast(xmlstring as xml)) as X(X)
cross apply X.X.nodes('/Holidays/Summer/Regions/Destinations/Destination') T(N)

SQL 小提琴

转换为 XML 可能存在性能问题.看看这个答案和这个答案

There might be performance issues with casting to XML. Have a look at this answer and this answer

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