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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1027) Create UDFs for XPath expression evaluation
Date Thu, 07 Jan 2010 19:50:54 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797769#action_12797769

Ning Zhang commented on HIVE-1027:

Thanks for the detailed explanations. It seems we are supporting XPath 1.0 here. When you
say "xpath() returns multiple nodes(list)", do you mean it returns a serialized XML string
representing the list of nodes such as <a>a1</a><a>a2</a> ...? In
this case, do you have a test case for composing xpath() functions. For example and subquery
returns XML string from the result of xpath() and the outer query takes that input to another
xpath*() function?

For (4) I'm sure whether we should interpret of empty list as empty string etc. We can definitely
define the mapping between the XML model to relation model this way, but it doesn't distinguish
the case where the xpath_string() result is an empty list or it is a single node but the value
of the node is empty (e.g., <a/> vs. no <a> element). 

Also all this information is better to be exposed to the wider community (not only developers)
as well. Can you also add all these to the Hive's wiki page? 

> Create UDFs for XPath expression evaluation
> -------------------------------------------
>                 Key: HIVE-1027
>                 URL: https://issues.apache.org/jira/browse/HIVE-1027
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Patrick Angeles
>            Assignee: Patrick Angeles
>            Priority: Minor
>         Attachments: hive-1027.patch, udf_xpath.patch
> Create UDFs for evaluating XPath expressions against XML documents.
> Examples:
> > SELECT xpath_double ('<a><b class="odd">1</b><b class="even">2</b><b
class="odd">4</b><c>8</c></a>', 'sum(a/b[@class="odd"])') FROM
src LIMIT 1 ;
> 5.0
> > SELECT xpath_string ('<a><b>b1</b><b>b2</b></a>',
'a/b[2]') FROM src LIMIT 1 ;
> b2
> > SELECT xpath ('<a><b>b1</b><b>b2</b><b>b3</b><c>c1</c><c>c2</c></a>',
'a/c/text()') FROM src LIMIT 1 ;
> ["c1","c2"]
> Included functions are: xpath_short, xpath_int, xpath_long, xpath_float, xpath_double/xpath_number,
xpath_string, xpath

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