SortMapping

SortMapping allows a developer to sort by a column other than the retrieval field column. For example, the following will cause the Title field to sort by the column FULL_TITLE instead of by the displayFieldSqlName (TITLE):

<CustomRetrievalField>
  <FieldRef levelType="ZBKS.Book" category="PDF">
    <FieldName>Title</FieldName>
  </FieldRef>
  <Type>MODEL_LINK</Type>
  <ModelLinkMapping surrogateIdSqlName="SYS_BOOK_ID" displayFieldSqlName="TITLE"/>
  <SortMapping sqlName="FULL_TITLE" type="STRING"/>
</CustomRetrievalField>	

Address and Composite retrieval fields are not sortable by default on UI. But you can provide SortMapping for these fields to make them sortable.