Question

More of reflection that a problem . Im creating a stored procedure that takes xml as an input parameter and having some issues when querying the data.

This is one of the queries

DECLARE @xVar XML
SET @xVar = 
  '<?xml version="1.0"?>
<Workflow xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://ait.com/workflow/">
  <Users>
    <User ObjectId="1232">
      <UserId>123</UserId>
    </User>
    <User ObjectId="1232">
      <UserId>124</UserId>
    </User>
  </Users>
</Workflow>';


WITH XMLNAMESPACES(DEFAULT 'http://ait.com/workflow/') 
SELECT  [UserId] = reportdata.item.value('UserId[1]', 'varchar(36)')

FROM   @xVar.nodes('//Workflow/Users/User') AS reportdata(item)  

This just returns the userid’s in the xml document . If i take a close look at the last part of the select statement

FROM   @xVar.nodes('//Workflow/Users/User') AS reportdata(item)  

It works and seems logical , start from the root and specify path, what is strange to me is that this also works

FROM   @xVar.nodes('//Users/User') AS reportdata(item)  

and even stranger that this works

FROM   @xVar.nodes('//User') AS reportdata(item)  

Probably missed some page in the XML Book for dummies, could someone enlighten me please

Answer 1

The double // means that it will give you all descendant nodes that match the expression.

This //Workflow/Users/User does not mean “start from the root”. An expression that matches from the root looks like this /Workflow/Users/User.

So //User will give you all descendant user nodes regardless of where they are.

Try this:

declare @XML xml = 
'<root>
  <user>1</user>
  <user>2</user>
  <child>
    <user>3</user>
  </child>
</root>'

select T.N.value('.',  'int') as Value
from @XML.nodes('//user') as T(N)

select T.N.value('.',  'int') as Value
from @XML.nodes('/user') as T(N)

select T.N.value('.',  'int') as Value
from @XML.nodes('/root/user') as T(N)

Result:

Value
-----------
1
2
3

(3 row(s) affected)

Value
-----------

(0 row(s) affected)

Value
-----------
1
2

(2 row(s) affected)