xml - XSL for-each and LEFT JOIN -

i need xslt statement gives me "left join": if selected node exist, return such nodes, otherwise loop once.

this different xsl:for-each loop, because when there not such node for-each loop returns 0 lines.

here pratical example.

xml file:

<root>     <sec1>         <x1/> ... <x1/>     </sec1>     <sec2>         <x2/> ... <x2/>     </sec2>     ...     <sec10>         <x10/> ... <x10/>     </sec10> </root> 

now, don't know how many "x1", "x2", .. "x10" have, , want print out possible combinations. easy , wrong solution:

<xsl:for-each select="/root/sec1/x1">     <xsl:for-each select="/root/sec2/x2">         ...         <xsl:for-each select="/root/sec10/x10">            ...print x1 , x2... , x10         </xsl:for-each>         ...     </xsl:for-each> </xsl:for-each> 

this solution wrong because, if there no "x3" returns 0 lines (just full join) while see other values (like left or right join).

i can use combination of xsl:choose, xls:when, xsl:foreach , xsl:otherwise, long.

i have tried build own xsl template, doesn't work:

<xsl:template name="left-join">     <xsl:param name="select"/>     <xsl:param name="template"/>      <xsl:choose>         <xsl:when test="$select">             <xsl:for-each select="$select">                 <xsl:call-template name="$templatename"> <!--wrong -->                     <xsl:with-param name="one-parameter" select="$select"/>                 </xsl:call-template>             </xsl:for-each>         </xsl:when>         <xsl:otherwise>             <xsl:call-template name="$templatename">                 <xsl:with-param name="one-parameter" select="$select"/>             </xsl:call-template>         </xsl:otherwise>     </xsl:choose> </xsl:template> 

even if don't understand question i'll try answer. understanding locking sql left join. (e.g. http://www.w3schools.com/sql/sql_join_left.asp) xml/xslt version following.

input data:

    <root>         <persons>             <person id="1">                 <name>hansen</name>             </person>             <person id="2">                 <name>svendson</name>             </person>             <person id="3">                 <name>pettersen</name>             </person>         </persons>         <orders>             <order id="1" >                 <p_id>3</p_id>                 <orderno>77895</orderno>             </order>             <order id="2">                 <p_id>3</p_id>                 <orderno>44678</orderno>             </order>             <order id="3">                 <p_id>1</p_id>                 <orderno>22456</orderno>             </order>             <order id="4">                 <p_id>1</p_id>                 <orderno>24562</orderno>             </order>             <order id="5">                 <p_id>15</p_id>                 <orderno>34764</orderno>             </order>         </orders>     </root> 

xslt

    <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/xsl/transform">         <xsl:output method="xml" version="1.0" encoding="utf-8" indent="yes"/>         <xsl:strip-space elements="*"/>          <xsl:template match="root">             <xsl:call-template name="person_order" />         </xsl:template>          <xsl:template name="person_order">            <orders>             <xsl:for-each select="//person">                 <xsl:variable name ="pid" select="@id" />                 <xsl:call-template name="left_join">                     <xsl:with-param name="jname" select="'order'"/>                     <xsl:with-param name="left" select="."/>                     <xsl:with-param name="right" select="//order[p_id = $pid]"/>                 </xsl:call-template>             </xsl:for-each>            </orders>         </xsl:template>           <xsl:template name="left_join">             <xsl:param name="jname" />             <xsl:param name="left" />             <xsl:param name="right" />              <xsl:choose>                 <xsl:when test="$right">                     <xsl:for-each select="$right">                         <xsl:call-template name="print_join">                             <xsl:with-param name="jname" select="$jname"/>                             <xsl:with-param name="left" select="$left"/>                             <xsl:with-param name="right" select="."/>                         </xsl:call-template>                     </xsl:for-each>                 </xsl:when>                 <xsl:otherwise>                     <xsl:call-template name="print_join">                         <xsl:with-param name="jname" select="$jname"/>                         <xsl:with-param name="left" select="$left"/>                      </xsl:call-template>                 </xsl:otherwise>             </xsl:choose>          </xsl:template>         <xsl:template match="node() | @*">             <xsl:copy>                 <xsl:apply-templates select="node() | @*"/>             </xsl:copy>         </xsl:template>          <xsl:template name="print_join">             <xsl:param name="jname" />             <xsl:param name="left" />             <xsl:param name="right" />             <xsl:element name="{$jname}" >                 <xsl:for-each select="$left">                     <xsl:apply-templates select="node() "/>                 </xsl:for-each>                 <xsl:if test="$right">                     <xsl:for-each select="$right">                         <xsl:apply-templates select="node() "/>                     </xsl:for-each>                 </xsl:if>             </xsl:element>         </xsl:template>      </xsl:stylesheet> 

which generates output:

    <orders>       <order>         <name>hansen</name>         <p_id>1</p_id>         <orderno>22456</orderno>       </order>       <order>         <name>hansen</name>         <p_id>1</p_id>         <orderno>24562</orderno>       </order>       <order>         <name>svendson</name>       </order>       <order>         <name>pettersen</name>         <p_id>3</p_id>         <orderno>77895</orderno>       </order>       <order>         <name>pettersen</name>         <p_id>3</p_id>         <orderno>44678</orderno>       </order>     </orders>