SELECT DBMS_XMLGEN.GETXML(
  'SELECT 25 as DF from dual
    '
    ) FROM dual;

with za as(
SELECT cast(25 as decimal(28)) as F1
, 'Привет' as F2
	)
select *
from za
FOR XML AUTO,XMLSCHEMA;

<xsd:schema targetNamespace="urn:schemas-microsoft-com:sql:SqlRowSet8" xmlns:schema="urn:schemas-microsoft-com:sql:SqlRowSet8" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:sqltypes="http://schemas.microsoft.com/sqlserver/2004/sqltypes" elementFormDefault="qualified">
  <xsd:import namespace="http://schemas.microsoft.com/sqlserver/2004/sqltypes" schemaLocation="http://schemas.microsoft.com/sqlserver/2004/sqltypes/sqltypes.xsd" />
  <xsd:element name="za">
    <xsd:complexType>
      <xsd:attribute name="F1">
        <xsd:simpleType>
          <xsd:restriction base="sqltypes:decimal">
            <xsd:totalDigits value="28" />
            <xsd:fractionDigits value="0" />
          </xsd:restriction>
        </xsd:simpleType>
      </xsd:attribute>
      <xsd:attribute name="F2" use="required">
        <xsd:simpleType>
          <xsd:restriction base="sqltypes:varchar" sqltypes:localeId="1033" sqltypes:sqlCompareOptions="IgnoreCase IgnoreKanaType IgnoreWidth" sqltypes:sqlSortId="106">
            <xsd:maxLength value="6" />
          </xsd:restriction>
        </xsd:simpleType>
      </xsd:attribute>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>
<za xmlns="urn:schemas-microsoft-com:sql:SqlRowSet8" F1="25" F2="Привет" />