You can use the XMLQUERY function to evaluate XQuery 1.0 queries against XML values. This example shows a query that is evaluated with the XML value as the context node:
SELECT XMLQUERY('for $i in /Customer/Order/Item
return $i/PartNumber' PASSING customerXML RETURNING CONTENT) as queryres
FROM customer WHERE customerID=1;
The result from the query is:
queryres ========================= <PartNumber>F54709</PartNumber><PartNumber>Z19743</PartNumber>