[basex-talk] XQuery - math on elements within a sequence

15 Jun 2015

      Hi everyone,
I'm trying to execute a XQuery sum function in a multiplication of two XML
elements, but it has been difficult to avoid the iteration in a sequence
of elements. For example, considering this case:

sample data:
<Orders>
     <Order>
        <OrderKey>1</OrderKey>
        <LineItem>
          <LineNumber>1</LineNumber>
          <ExtendedPrice>70848.0000</ExtendedPrice>
          <Discount>0.0913</Discount>
          <ReturnFlag>A</ReturnFlag>
          <LineStatus>F</LineStatus>
          <ShipDate>1994-09-03</ShipDate>
        </LineItem>
        <LineItem>
          <LineNumber>2</LineNumber>
          <ExtendedPrice>64372.0000</ExtendedPrice>
          <Discount>0.0674</Discount>
          <ReturnFlag>A</ReturnFlag>
          <LineStatus>F</LineStatus>
          <ShipDate>1994-08-18</ShipDate>
        </LineItem>
        <LineItem>
          <LineNumber>3</LineNumber>
          <ExtendedPrice>64247.0000</ExtendedPrice>
          <Discount>0.0396</Discount>
          <ReturnFlag>R</ReturnFlag>
          <LineStatus>F</LineStatus>
          <ShipDate>1994-10-21</ShipDate>
        </LineItem>
      </Order>
      . . .
</Orders>

XQuery:
<results> {
   for $lineitem in collection("tpch")/Orders/Order/LineItem
   let $returnflag := $lineitem/ReturnFlag
   let $linestatus := $lineitem/LineStatus
   where $lineitem/ShipDate <= "1998-08-31"
   group by $returnflag, $linestatus
   order by $returnflag, $linestatus
   return
   <record>
      <sum_disc_price>{sum($lineitem/ExtendedPrice*(1-$lineitem/Discount))}</sum_disc_price>
   </record>
} </results>

BaseX output:
[XPTY0004] Item expected, sequence found: (element ExtendedPrice {...},
......

My question: Considering this dataset model, how can I to write this query
without change its semantics?

I wouldn't want to use extra functions (e.g., fn:for-each), because I need
to submit the same query in an limited xquery processor.

Thanks in advance!

-- 
Luiz Matos
PhD student at Federal Fluminense University