How do I remove redundant namespace in nested query when using FOR XML PATH

Question

UPDATE: I\'ve discovered there is a Microsoft Connect item raised for this issue here

When using FOR XML PATH

Answer 1

It would be really nice if FOR XML PATH actually worked more cleanly. Reworking your original example with @table variables:

declare @t1 table (c1 int, c2 varchar(50));
declare @t2 table (c1 int, c2 int, c3 varchar(50));
insert @t1 values 
    (1, 'Mouse'),
    (2, 'Chicken'),
    (3, 'Snake');
insert @t2 values
    (1, 1, 'Front Right'),
    (2, 1, 'Front Left'),
    (3, 1, 'Back Right'),
    (4, 1, 'Back Left'),
    (5, 2, 'Right'),
    (6, 2, 'Left');

;with xmlnamespaces( default 'uri:animal')
select  a.c2 as "@species",
    (
        select  l.c3 as "text()"
        from    @t2 l
        where   l.c2 = a.c1
        for xml path('leg'), type
    ) as "legs"
from @t1 a
for xml path('animal'), root('zoo');

Yields the problem XML with repeated namespace declarations:

  
    
      Front Right
      Front Left
      Back Right
      Back Left
    
  
  
    
      Right
      Left
    
  
  

You can migrate elements between namespaces using XQuery with wildcard namespace matching (that is, *:elementName), as below, but it can be quite cumbersome for complex XML:

;with xmlnamespaces( default 'http://tempuri.org/this/namespace/is/meaningless' )
select (
    select  a.c2 as "@species",
        (
            select  l.c3 as "text()"
            from    @t2 l
            where   l.c2 = a.c1
            for xml path('leg'), type
        ) as "legs"
    from @t1 a
    for xml path('animal'), root('zoo'), type
).query('declare default element namespace "uri:animal";

{ for $a in *:zoo/*:animal return
    
    {attribute species {$a/@species}}
    { for $l in $a/*:legs return
        
        { for $m in $l/*:leg return
            { $m/text() }
        }
    }
}');

Which yields your desired result:

  
    
      Front Right
      Front Left
      Back Right
      Back Left
    
  
  
    
      Right
      Left