Group By in xquery - sql

Question

I am trying to convert the following code to xquery so that the results remain the same. I am trying to calculate the total freight costs for each customer
SELECT
c.CompanyName, SUM(o.freight) AS [Total Freight Costs]
FROM
Customers c, Orders o
WHERE
c.CustomerID = o.CustomerID
GROUP BY
CompanyName
The test data for the customers.xml and orders are as follows
<dataroot>
<Customers>
<CustomerID>ALFKI</CustomerID>
<CompanyName>Alfreds Futterkiste</CompanyName>
<ContactName>Maria Anders</ContactName>
<ContactTitle>Sales Representative</ContactTitle>
<Address>Obere Str. 57</Address>
<City>Berlin</City>
<PostalCode>12209</PostalCode>
<Country>Germany</Country>
<Phone>030-0074321</Phone>
<Fax>030-0076545</Fax>
</Customers>
<Customers>
<CustomerID>ANATR</CustomerID>
<CompanyName>Ana Trujillo Emparedados y helados</CompanyName>
<ContactName>Ana Trujillo</ContactName>
<ContactTitle>Owner</ContactTitle>
<Address>Avda. de la Constitución 2222</Address>
<City>México D.F.</City>
<PostalCode>05021</PostalCode>
<Country>Mexico</Country>
<Phone>(5) 555-4729</Phone>
<Fax>(5) 555-3745</Fax>
</Customers>
</dataroot>
Orders.xml
<dataroot>
<Orders>
<OrderID>10248</OrderID>
<CustomerID>WILMK</CustomerID>
<EmployeeID>5</EmployeeID>
<OrderDate>1996-07-04T00:00:00</OrderDate>
<RequiredDate>1996-08-01T00:00:00</RequiredDate>
<ShippedDate>1996-07-16T00:00:00</ShippedDate>
<ShipVia>3</ShipVia>
<Freight>32.38</Freight>
<ShipName>Vins et alcools Chevalier</ShipName>
<ShipAddress>59 rue de l&apos;Abbaye</ShipAddress>
<ShipCity>Reims</ShipCity>
<ShipPostalCode>51100</ShipPostalCode>
<ShipCountry>France</ShipCountry>
</Orders>
</dataroot>
This is what I have so far
for $o in doc("Orders.xml")/dataroot/Orders,
$c in doc("Customers.xml")/dataroot/Customers[CustomerID = $o/CustomerID]
return
<OrderDetails>
{
$c/CompanyName,
sum($o/Freight)
}
</OrderDetails>

Answer 1

Simple enough:
(: select only customers with at least one order :)
for $c in doc("Customers.xml")/dataroot/Customers
[doc("Orders.xml")/dataroot/Orders/CustomerID=./CustomerID]
(: get the list of orders for this customer :)
let $o := doc("Orders.xml")/dataroot/Orders[CustomerID = $c/CustomerID]
(: ...and properly encapsulate the calculated value in the result :)
return
<OrderDetails>
{$c/CompanyName}
<TotalFreight>{sum($o/Freight)}</TotalFreight>
</OrderDetails>
The test data you gave has no matching CustomerIDs, however, so it returns nothing for this query; I had to mock up my own. With that done, however, I get output akin to the following:
<OrderDetails>
<CompanyName>Alfreds Futterkiste</CompanyName>
<TotalFreight>45.58</TotalFreight>
</OrderDetails>

Answer 2

Actually, since XQuery 3.0 there is a standardized "group by" for FLWOR expressions.