How to preserve an ampersand (&) while using FOR X

问题:

Are there any tricks for preventing SQL Server from entitizing chars like &, <, and >? I'm trying to output a URL in my XML file but SQL wants to replace any '&' with '&'

Take the following query:

SELECT 'http://foosite.com/' + RTRIM(li.imageStore)
        + '/ImageStore.dll?id=' + RTRIM(li.imageID)
        + '&raw=1&rev=' + RTRIM(li.imageVersion) AS imageUrl
FROM ListingImages li
FOR XML PATH ('image'), ROOT ('images'), TYPE

The output I get is like this (&s are entitized):

<images>
  <image>
    <imageUrl>http://foosite.com/pics4/ImageStore.dll?id=7E92BA08829F6847&amp;raw=1&amp;rev=0</imageUrl>
  </image>
</images>

What I'd like is this (&s are not entitized):

<images>
  <image>
    <imageUrl>http://foosite.com/pics4/ImageStore.dll?id=7E92BA08829F6847&raw=1&rev=0</imageUrl>
  </image>
</images>

How does one prevent SQL server from entitizing the '&'s into '&'?

回答1:

What SQL Server generates is correct. What you expect to see is not well-formed XML. The reason is that & character signifies the start of an entity reference, such as &. See the XML specification for more information.

When your XML parser parses this string out of XML, it will understand the & entity references and return the text back in the form you want. So the internal format in the XML file should not cause a problem to you unless you're using a buggy XML parser, or trying to parse it manually (in which case your current parser code is effectively buggy at the moment with respect to the XML specification).

回答2:

There are situations where a person may not want well formed XML - the one I (and perhaps the original poster) encountered was using the For XML Path technique to return a single field list of 'child' items via a recursive query. More information on this technique is here (specifically in the 'The blackbox XML methods' section): Concatenating Row Values in Transact-SQL

For my situation, seeing 'H&E' (a pathology stain) transformed into 'well formed XML' was a real disappointment. Fortunately, I found a solution... the following page helped me solve this issue relatively easily and without having re-architect my recursive query or add additional parsing at the presentation level (for this as well for as other/future situations where my child-rows data fields contain reserved XML characters): Handling Special Characters with FOR XML PATH

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EDIT: code below from the referenced blog post.

select
  stuff(
     (select ', <' + name + '>'
     from sys.databases
     where database_id > 4
     order by name
     for xml path(''), root('MyString'), type
     ).value('/MyString[1]','varchar(max)')
   , 1, 2, '') as namelist;

回答3:

Try this....

select 
  stuff( 
     (select ', <' + name + '>' 
     from sys.databases 
     where database_id > 4 
     order by name 
     for xml path(''), root('MyString'), type 
     ).value('/MyString[1]','varchar(max)') 
   , 1, 2, '') as namelist;