Processing XML prolog by SQL Server XML functions - sql-server

Question

I have a large database table with an XML column. The XML contents is a kind of document like as below:
<?int-dov version="1.0" encoding="UTF-8" standalone="no"?>
<ds:datastoreItem ds:itemID="{F8484AF4-73BF-45CA-A524-0D796F244F37}" xmlns:ds="http://schemas.openxmlformats.org/officeDocument/2006/customXml"><ds:schemaRefs><ds:schemaRef ds:uri="http://schemas.openxmlformats.org/officeDocument/2006/bibliography"/></ds:schemaRefs></ds:datastoreItem>
I'm seeking a function or fast way to fetch standalone attribute value in a T-SQL query. When I run the below query:
select XmlContent.query('#standalone') from XmlDocuments
I get this error message:
Msg 2390, Level 16, State 1, Line 4
XQuery [XmlDocuments.XmlContent.query()]: Top-level attribute nodes are not supported
So, I would be appreciated if anybody gives me a solution to address this problem.

Answer 1

You can use the processing-instruction() function to get that.
SELECT #xml.value('./processing-instruction("int-dov")[1]','nvarchar(max)')
Result
version="1.0" encoding="UTF-8" standalone="no"
If you want to get just the standalone part, the only way I've found is to construct an XML node from it:
SELECT CAST(
N'<x ' +
#xml.value('./processing-instruction("int-dov")[1]','nvarchar(max)') +
N' />' AS xml).value('x[1]/#standalone','nvarchar(10)'
Result
no
db<>fiddle

Answer 2

Just to complement #Charlieface answer. All credit goes to him.
SQL
DECLARE #xml XML =
N'<?int-dov version="1.0" encoding="UTF-8" standalone="no"?>
<ds:datastoreItem ds:itemID="{F8484AF4-73BF-45CA-A524-0D796F244F37}"
xmlns:ds="http://schemas.openxmlformats.org/officeDocument/2006/customXml">
<ds:schemaRefs>
<ds:schemaRef ds:uri="http://schemas.openxmlformats.org/officeDocument/2006/bibliography"/>
</ds:schemaRefs>
</ds:datastoreItem>';
SELECT col.value('x[1]/#standalone','nvarchar(10)') AS [standalone]
, col.value('x[1]/#encoding','nvarchar(10)') AS [encoding]
, col.value('x[1]/#version','nvarchar(10)') AS [version]
FROM (VALUES(CAST(N'<x ' +
#xml.value('./processing-instruction("int-dov")[1]','nvarchar(max)') +
N' />' AS xml))
) AS tab(col);
Output
+------------+----------+---------+
| standalone | encoding | version |
+------------+----------+---------+
| no | UTF-8 | 1.0 |
+------------+----------+---------+