-20338 THE DATA TYPE OF EITHER THE SOURCE OR TARGET OPERAND OF AN XMLCAST SPECIFICATION MUST BE XML

Explanation
 The XMLCAST specification must have one operand
that has the data type XML. The XMLCAST operation can be from one
the following: an XML type value to an SQL type value
from an SQL type value to and XML type value

The XMLCAST specification also accepts having both the source
and target operands as XML, but if you specify the source and target
operands as XML, then no actual casting operation is performed. 

System action
 The expression cannot be processed.

Programmer response
If both operands are SQL data types other
than XML, then use the CAST specification. Otherwise, change the XMLCAST
specification so that at least one operand is the XML data type.

SQLSTATE
42815