adding encoding information to the result of FOR XML [duplicate]

Answer 1

As @gbn points out in another answer and on another question, "the XML data is stored internally as ucs-2", and SQL Server doesn't include it when producing the data. However, you can convert the XML to a string and append the XML declaration at the beginning manually. However, simply using UTF-8 in the declaration would be inaccurate. The Unicode string which SQL produces is in UCS-2. For example, this will fail:

SELECT CONVERT(xml,N'' + CONVERT(NVARCHAR(MAX),CONVERT(XML,N'' + NCHAR(10176) + N'')));

with error:

Msg 9402, Level 16, State 1, Line 1 XML parsing: line 1, character 38, unable to switch the encoding

This, on the other hand, will work as expected:

SELECT CONVERT(xml,N'' + CONVERT(NVARCHAR(MAX),CONVERT(XML,N'' + NCHAR(10176) + N'')));

Here is code which will produce the full, declaration-laden XML string you seek for your example data:

DECLARE @Agents TABLE
(
    AgentID int,
    AgentName nvarchar(50),
    AgentLocation nvarchar(100)
);
INSERT INTO @Agents (AgentID, AgentName, AgentLocation) VALUES (1, N'Mike', N'Sanfrancisco');
INSERT INTO @Agents (AgentID, AgentName, AgentLocation) VALUES (2, N'John', N'NY');

WITH BaseData AS
(
    SELECT
        (
            SELECT
                AgentID AS '@id',
                AgentName AS 'Name',
                AgentLocation AS 'Location'
            FROM    @Agents
            FOR     XML PATH('Agent'), ROOT('Agents'), TYPE
        ) AS AgentXML
), FullStringTable AS
(
    SELECT
        *,
        '' +
        CONVERT(nvarchar(max),AgentXML) AS FullString
    FROM        BaseData
)
SELECT
    AgentXML AS OriginalXML,
    FullString,
    CONVERT(xml,FullString) AS FullStringConvertedToXML
FROM        FullStringTable;