SQL server 2012 parsing XML with namespaces - sql

Question

I have a table containing rows of xml in the following format:
<msit:message xmlns:wsa="http://URL1" xmlns:msit="http://URL2" xmlns:env="http://URL3">
<env:Body>
<ns0:parent xmlns:ns0="http://URL4">
<ns0:child>123456789</ns0:child>
...
</ns0:parent>
</env:Body>
</msit:message>`
in a table name mytable, column name data.
I have written the following query:
;with xmlnamespaces('http://URL2' as msit,
'http://URL3' as env,
'http://URL1' as wsa,
'http://URL4' as ns0)
select
t2.field.value('child[1]','varchar(20)') as ban
from mytable
cross apply data.nodes('/message/Body/parent') t2(field)
it returns empty set, when I need to return 123456789
What am I doing wrong ?
Thank you

Answer 1

you may need to include the prefixes in the xpath expressions:
declare #mytable table (data xml)
insert into #mytable values
('<msit:message xmlns:wsa="http://URL1" xmlns:msit="http://URL2" xmlns:env="http://URL3">
<env:Body>
<ns0:parent xmlns:ns0="http://URL4">
<ns0:child>123456789</ns0:child>
</ns0:parent>
</env:Body>
</msit:message>')
;with xmlnamespaces('http://URL2' as msit,
'http://URL3' as env,
'http://URL1' as wsa,
'http://URL4' as ns0)
select
t2.field.value('ns0:child[1]','varchar(20)') as ban
from #mytable
cross apply data.nodes('/msit:message/env:Body/ns0:parent') t2(field)

Answer 2

The whole point of namespaces is to differentiate between elements that were brought together from multiple documents.
It is similar to the way we qualify columns with tables' names or aliases, e.g. t1.x Vs. t2.x.
So when you refer to an element you should qualify it with the right namespace.
You might also want to use outer apply instead of cross apply in case there's a missing element.
create table mytable (x xml);
insert into mytable (x) values
(
'
<msit:message xmlns:wsa="http://URL1" xmlns:msit="http://URL2" xmlns:env="http://URL3">
<env:Body>
<ns0:parent xmlns:ns0="http://URL4">
<ns0:child>123456789</ns0:child>
</ns0:parent>
</env:Body>
</msit:message>
'
)
;
;
with xmlnamespaces
(
'http://URL2' as msit
,'http://URL3' as env
,'http://URL1' as wsa
,'http://URL4' as ns0
)
select t2.field.value('ns0:child[1]','varchar(20)') as ban
from mytable
outer apply x.nodes('/msit:message/env:Body/ns0:parent') t2(field)
;