How to add a new column/field to an existing composite primary key
<changeSet author="yours_truly" id="EXAMPLE-02-01-dropPK">
<dropPrimaryKey tableName= "our_awesome_table" constraintName="CPK_OUR_AWESOME_TABLE"/>
</changeSet>
<changeSet author="yours_truly" id="EXAMPLE-02-01-addNNcol">
<addColumn tableName="our_awesome_table">
<column name="CREATED_AT" type="datetime" valueDate="current_datetime" defaultValueDate="current_datetime">
<constraints nullable="false"/>
</column>
</addColumn>
</changeSet>
<changeSet author="yours_truly" id="EXAMPLE-02-02">
<addPrimaryKey tableName="our_awesome_table" columnNames="source,external_id,CREATED_AT" constraintName="CPK_OUR_AWESOME_TABLE"/>
</changeSet>