Any documention available on XML DB Queries?

Question

Hi,
I was searching to find some documentation and examples on queries to retrieve the data from XMLType Coloumns.
The problem is I found some documentation which has examples on how to retrieve data from plain XML.
But my XML's are different as they have more than one namespace in each xml so normal xpath queries doesn't work on namespace based xmls.
Would appreciate if someone help me.
Thanks

Answer 1

Depending upon what documentation you've looked at, the answer may have been presented, just not shown as a clear example.
If you look at ExtractValue documentation, you will notice a third parm. This is where you put namespace information from the XML that the XPath uses. You don't need to put all your namespaces from the XML, just the ones that your XPath references. This third parm also exists for Extract and resides in a different format for XMLTable, as shown in the FAQ for this forum.
As a simple example of how it looks, here is a sample query using two namespaces
WITH base_t AS
(SELECT XMLTYPE('<a:root xmlns:a="http://madeup.com/a" xmlns:b="http://madeup.com/b">
<b:child>hi</b:child></a:root>') tab_col
   FROM DUAL)
SELECT extractValue(tab_col,'a:root/b:child','xmlns:a="http://madeup.com/a" xmlns:b="http://madeup.com/b"') rslt
  FROM base_t;You can also do
SELECT extractValue(tab_col,'//b:child','xmlns:b="http://madeup.com/b"') rslt
  FROM base_t;which shows just using the one namespace.
And since I was at it, here is the XMLTable version
SELECT x.rslt
  FROM base_t,
       XMLTABLE(XMLNAMESPACES('http://madeup.com/a' AS "a",
                              'http://madeup.com/b' AS "b"),
                '/a:root'
                PASSING base_t.tab_col
                COLUMNS 
                rslt VARCHAR2(5)  PATH 'b:child') x;Hope all that helps.