Use ampersand in CAST in SQL

问题

The following code snippet on SQL server 2005 fails on the ampersand '&':

select cast('<name>Spolsky & Atwood</name>' as xml)

Does anyone know a workaround?

Longer explanation, I need to update some data in an XML column, and I'm using a search & replace type hack by casting the XML value to a varchar, doing the replace and updating the XML column with this cast.

回答1:

select cast('<name>Spolsky &amp; Atwood</name>' as xml)

A literal ampersand inside an XML tag is not allowed by the XML standard, and such a document will fail to parse by any XML parser.

An XMLSerializer() will output the ampersand HTML-encoded.

The following code:

using System.Xml.Serialization;

namespace xml
{
    public class MyData
    {
        public string name = "Spolsky & Atwood";
    }

    class Program
    {
        static void Main(string[] args)
        {
            new XmlSerializer(typeof(MyData)).Serialize(System.Console.Out, new MyData());
        }
    }
}

will output the following:

<?xml version="1.0" encoding="utf-8"?>
<MyData
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <name>Spolsky &amp; Atwood</name>
</MyData>

, with an & instead of &.

回答2:

It's not valid XML. Use &:

select cast('<name>Spolsky &amp; Atwood</name>' as xml)

回答3:

You'd need to XML escape the text, too.

So let's backtrack and assume you're building that string as:

SELECT '<name>' + MyColumn + '</name>' FROM MyTable

you'd want to do something more like:

SELECT '<name>' + REPLACE( MyColumn, '&', '&amp;' ) + '</name>' FROM MyTable

Of course, you probable should cater for the other entities thus:

SELECT '<name>' + REPLACE( REPLACE( REPLACE( REPLACE( REPLACE( MyColumn, '&', '&amp;' ), '''', '&apos;' ), '"', '&quot;' ), '<', '&lt;' ), '>', '&gt;' ) + '</name>' FROM MyTable

回答4:

When working with XML in SQL you're a lot safer using built-in functions instead of converting it manually.

The following code will build a proper SQL XML variable that looks like your desired output based on a raw string:

DECLARE @ExampleString nvarchar(40)
    , @ExampleXml xml

SELECT  @ExampleString = N'Spolsky & Atwood'

SELECT  @ExampleXml =
    (
        SELECT  'Spolsky & Atwood' AS 'name'
        FOR XML PATH (''), TYPE
    )

SELECT  @ExampleString , @ExampleXml

回答5:

As John and Quassnoi state, & on it's own is not valid. This is because the ampersand character is the start of a character entity - used to specify characters that cannot be represented literally. There are two forms of entity - one specifies the character by name (e.g., &, or "), and one the specifies the character by it's code (I believe it's the code position within the Unicode character set, but not sure. e.g., " should represent a double quote).

Thus, to include a literal & in a HTML document, you must specify it's entity: &. Other common ones you may encounter are < for <, > for >, and " for ".

来源：https://stackoverflow.com/questions/1119310/use-ampersand-in-cast-in-sql

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sql

sql-server

xml

casting

ampersand