If a view transformation contains a union of a multi-source model and a non multisource model, because of https://issues.jboss.org/browse/TEIID-4728 the SOURCE_NAME column has to be created on the View and hence on the non-multisource model and if you don't mark that source model as multisource the SOURCE_NAME column is pushed to the source.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<vdb name="multi_emp" version="1">
<description/>
<property name="validationDateTime" value="Mon Oct 31 08:01:36 CDT 2016"/>
<property name="validationVersion" value="8.12.6"/>
<model name="multi" type="PHYSICAL" visible="true">
<property name="multisource" value="true"/>
<!-- optional properties -->
<property name="multisource.columnName" value="SOURCE_NAME"/>
<property name="multisource.addColumn" value="true"/>

<source connection-jndi-name="java:/deb" name="deb" translator-name="postgresql"/>
<source connection-jndi-name="java:/dv63" name="dv63" translator-name="postgresql"/>
<metadata type="DDL"><![CDATA[
CREATE FOREIGN TABLE emp (
id integer NOT NULL OPTIONS(NAMEINSOURCE '"id"', NATIVE_TYPE 'int4', CASE_SENSITIVE 'FALSE', FIXED_LENGTH 'TRUE', SEARCHABLE 'ALL_EXCEPT_LIKE'),
name string(2147483647) OPTIONS(NAMEINSOURCE '"name"', NATIVE_TYPE 'text'),
SOURCE_NAME string(50),
CONSTRAINT pk_emp PRIMARY KEY(id)
) OPTIONS(UPDATABLE 'true',NAMEINSOURCE '"public"."emp"')
]]></metadata>
</model>
<model name="Debbiedb" type="PHYSICAL" visible="true">
<!-- Have to add this to make it work <property name="multisource" value="true"/> -->
<source connection-jndi-name="java:/debbiedb" name="debbiedb" translator-name="postgresql"/>
<metadata type="DDL"><![CDATA[
CREATE FOREIGN TABLE mytable (
id integer NOT NULL OPTIONS(NAMEINSOURCE '"id"', NATIVE_TYPE 'int4', CASE_SENSITIVE 'FALSE', FIXED_LENGTH 'TRUE', SEARCHABLE 'ALL_EXCEPT_LIKE'),
name string(2147483647) OPTIONS(NAMEINSOURCE '"name"', NATIVE_TYPE 'text'),
age integer OPTIONS(NAMEINSOURCE '"age"', NATIVE_TYPE 'int4', CASE_SENSITIVE 'FALSE', FIXED_LENGTH 'TRUE', SEARCHABLE 'ALL_EXCEPT_LIKE'),
address string(2147483647) OPTIONS(NAMEINSOURCE '"address"', NATIVE_TYPE 'text'),
SOURCE_NAME string(50),
CONSTRAINT pk_id PRIMARY KEY(id)
) OPTIONS(UPDATABLE 'true',NAMEINSOURCE '"public"."mytable"')
]]></metadata>
</model>
<model name="Debbiev" type="VIRTUAL" visible="true">
<property name="imports" value="Debbiedb"/>
<property name="imports" value="multi"/>
<metadata type="DDL"><![CDATA[
CREATE VIEW comboview (
id integer,
name string(100),
SOURCE_NAME string(50)
)
AS
SELECT id,name,SOURCE_NAME FROM multi.emp UNION ALL SELECT id, name, SOURCE_NAME FROM Debbiedb.mytable
]]></metadata>
</model>
</vdb>