Можно использовать дополнительную информацию о вашей проблеме, но здесь идет речь:
SELECT TOP 10 SomeId, COUNT(1) SomeValue
INTO #SomeTable
FROM (SELECT ABS(CAST(NEWID() AS binary(6)) % 1000) + 1 SomeId
FROM sysobjects) sample
GROUP BY SomeId;
WITH XMLNAMESPACES (N'http://www.w3.org/2001/XMLSchema-instance' as xsi)
SELECT SomeId "@SomeId",
-- here is where you specify the type to put in the attribute
'table' "@xsi:type",
SomeValue
FROM #SomeTable
FOR XML PATH('AnElement'), ROOT('RootElement')
DROP TABLE #SomeTable;