How to use Group By in Marklogic? - group-by

Question

I want to use Group By in xquery. Can someone tell me please how to use Group By in Marklogic ?

Answer 1

Alternatively, you could call out to XSLT using xdmp:xslt-invoke or xdmp:xslt-eval. MarkLogic's XSLT processor supports XSLT 2.0, which includes full support for <xsl:for-each-group>.

Answer 2

The short answer is to use map:map. See http://docs.marklogic.com/map:map for documentation, and http://blakeley.com/blogofile/archives/560/ for a longer discussion.

Answer 3

xquery version "1.0-ml";
let $xml:= <Students>
<Student Country="England" Name="Dan" Age="20" Class="C"/>
<Student Country="England" Name="Maria" Age="20" Class="B" />
<Student Country="Australia" Name="Mark" Age="22" Class="A" />
</Students>
let $xsl:= <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:fn="http://www.w3.org/2005/xpath-functions">
<xsl:template match="Students">
<result>
<xsl:for-each-group select="Student" group-by="#Country">
<country>
<xsl:attribute name="name"><xsl:value-of select="fn:current-grouping-key()"/></xsl:attribute>
<xsl:for-each select="fn:current-group()/#Name">
<name><xsl:value-of select="."/></name>
</xsl:for-each>
</country>
</xsl:for-each-group>
</result>
</xsl:template>
</xsl:stylesheet>
return xdmp:xslt-eval($xsl,$xml)

Answer 4

MarkLogic covers parts of XQuery 3.0 (with its 1.0-ml dialect), but unfortunately FLWOR group by support is lacking.
However, you can still programmatically create group by like syntax which will achieve the same results. Here is an XQuery example:
for $d in distinct-values(doc("order.xml")//item/#dept)
let $items := doc("order.xml")//item[#dept = $d]
order by $d
return <department code="{$d}">{
for $i in $items
order by $i/#num
return $i
}</department>
HTH