How can I match the xmlns:* attributes with SQL? - sql-server

Question

Question
Is there any way to use XPath which matches on the namespace axis in SQL Server? i.e. I'm aware that SQL does not natively support this axis; but is there any query which would be functionally similar which may work?
Context
I'm hoping to write code to debloat duplicate namespaces from my XML, leaving only those declarations which exist on the root element. I've seen various other solutions for this, but all are quite painful; so I investigated alternate solutions & in doing so realised that SQL does not support the namespace axis.
declare #demo xml = '
<hello:a xmlns:hello="test" xmlns:world="me">
<hello:b>
<world:c xmlns:world="me">demo</world:c>
<hello:d xmlns:hello="test">demo</hello:d>
<world:e xmlns:hello="test" xmlns:world="me">demo</world:e>
<hello:f xmlns:hello="test" xmlns:world="me" world:demo=''x''>demo</hello:f>
</hello:b>
</hello:a>
'
set #demo.modify('delete (/*//namespace::*)')
--set #demo.modify('delete (/*//#*[not(namespace-uri() > "")])') --tried just in case xmlns is treated as an attribute in SQL; no joy :/
select #demo
Research
NB: There's a similar question asking how this is done in XSLT; but SQL-Server does not include the namespace:: axis. A list of the available axes in SQL is available here.
There are other ways to remove this bloat; but none are that straightforwards, and these posts are now quite dated, hence my researching alternate approaches:
a good overview of the various available methods: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/2f7bdfbf-8e40-456b-84e8-195318649703/how-to-remove-namespaces-from-xml-tags-when-using-for-xml-option-with-xmlnamespaces?forum=transactsql&prof=required
a few answers on how to avoid this issue when generating the XML within SQL How do I remove redundant namespace in nested query when using FOR XML PATH
Current Solution
NB: Since I've been unable to find a straight forwards solution, my current method for removing these namespaces is as below. There are some risks with this (e.g. losing attributes on the root element, issues if the expected spaces are missing / other whitespace characters are used instead), but this is good enough for my purposes, if very hacky & non-generic.
declare #demo xml = '
<hello:a xmlns:hello="test" xmlns:world="me">
<hello:b>
<world:c xmlns:world="me">demo</world:c>
<hello:d xmlns:hello="test">demo</hello:d>
<world:e xmlns:hello="test" xmlns:world="me">demo</world:e>
<hello:f xmlns:hello="test" xmlns:world="me" world:demo=''x''>demo</hello:f>
</hello:b>
</hello:a>
'
;with xmlnamespaces('test' as hello, 'me' as world)
select #demo = cast(
'<hello:a xmlns:hello="test" xmlns:world="me">'
+ replace(
replace(
cast(#demo.query('/*/*') as nvarchar(max))
,' xmlns:hello="test"'
,''
)
,' xmlns:world="me"'
,''
)
+ '</hello:a>'
as xml
)
select #demo

Answer 1

SQL-Server's abilities to deal with XML namespaces is really - uhm - painful...
the only way I know to define namespaces just as you want them is FOR XML EXPLICIT (unless you want to walk the string-manipulation route...)
You can create the XML you want with:
SELECT 1 AS Tag
,NULL AS Parent
,'test' AS [hello:a!1!xmlns:hello]
,'me' AS [hello:a!1!xmlns:world]
,NULL AS [hello:b!2]
,NULL AS [world:c!3]
,NULL AS [hello:d!4]
,NULL AS [world:e!5]
,NULL AS [hello:f!6]
,NULL AS [hello:f!6!world:demo]
UNION ALL
SELECT 2
,1
,NULL
,NULL
,''
,NULL
,NULL
,NULL
,NULL
,NULL
UNION ALL
SELECT 3
,2
,NULL
,NULL
,''
,'demo'
,NULL
,NULL
,NULL
,NULL
UNION ALL
SELECT 4
,2
,NULL
,NULL
,''
,NULL
,'demo'
,NULL
,NULL
,NULL
UNION ALL
SELECT 5
,2
,NULL
,NULL
,''
,NULL
,NULL
,'demo'
,NULL
,NULL
UNION ALL
SELECT 6
,2
,NULL
,NULL
,''
,NULL
,NULL
,NULL
,'demo'
,'x'
FOR XML EXPLICIT;
The result
<hello:a xmlns:hello="test" xmlns:world="me">
<hello:b>
<world:c>demo</world:c>
<hello:d>demo</hello:d>
<world:e>demo</world:e>
<hello:f world:demo="x">demo</hello:f>
</hello:b>
</hello:a>
As Jeroen Mostert has pointed out in comments you might use outdated FROM OPEN XML like here:
declare #demo xml =
'<hello:a xmlns:hello="test" xmlns:world="me">
<hello:b>
<world:c xmlns:world="me">demo</world:c>
<hello:d xmlns:hello="test">demo</hello:d>
<world:e xmlns:hello="test" xmlns:world="me">demo</world:e>
<hello:f xmlns:hello="test" xmlns:world="me" world:demo=''x''>demo</hello:f>
</hello:b>
</hello:a>';
DECLARE #hdoc int;
EXEC sp_xml_preparedocument #hdoc OUTPUT, #demo;
SELECT *
FROM OPENXML(#hdoc, '//*');
EXEC sp_xml_removedocument #hdoc;
GO
The result
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| id | parentid | nodetype | localname | prefix | namespaceuri | datatype | prev | text |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 0 | NULL | 1 | a | hello | test | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 2 | 0 | 2 | hello | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 20 | 2 | 3 | #text | NULL | NULL | NULL | NULL | test |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 3 | 0 | 2 | world | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 21 | 3 | 3 | #text | NULL | NULL | NULL | NULL | me |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 4 | 0 | 1 | b | hello | test | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 5 | 4 | 1 | c | world | me | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 6 | 5 | 2 | world | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 22 | 6 | 3 | #text | NULL | NULL | NULL | NULL | me |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 7 | 5 | 3 | #text | NULL | NULL | NULL | NULL | demo |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 8 | 4 | 1 | d | hello | test | NULL | 5 | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 9 | 8 | 2 | hello | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 23 | 9 | 3 | #text | NULL | NULL | NULL | NULL | test |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 10 | 8 | 3 | #text | NULL | NULL | NULL | NULL | demo |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 11 | 4 | 1 | e | world | me | NULL | 8 | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 12 | 11 | 2 | hello | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 24 | 12 | 3 | #text | NULL | NULL | NULL | NULL | test |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 13 | 11 | 2 | world | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 25 | 13 | 3 | #text | NULL | NULL | NULL | NULL | me |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 14 | 11 | 3 | #text | NULL | NULL | NULL | NULL | demo |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 15 | 4 | 1 | f | hello | test | NULL | 11 | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 16 | 15 | 2 | hello | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 26 | 16 | 3 | #text | NULL | NULL | NULL | NULL | test |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 17 | 15 | 2 | world | xmlns | NULL | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 27 | 17 | 3 | #text | NULL | NULL | NULL | NULL | me |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 18 | 15 | 2 | demo | world | me | NULL | NULL | NULL |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 28 | 18 | 3 | #text | NULL | NULL | NULL | NULL | x |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
| 19 | 15 | 3 | #text | NULL | NULL | NULL | NULL | demo |
+----+----------+----------+-----------+--------+--------------+----------+------+------+
This table includes all the information you would need to create the statement above in a recursive CTE dynamically and use EXEC to create the XML from scratch.
with WHERE nodetype=1 you get the elements, with 2 the attributes...
But - to be honest - this is a huge effort...
If your XMLs are more complicated, nested, whatever, this will get really bad...