Fields named in KEY IS phrases of SELECT statements are included as column names. Other fields that occupy the same areas as the key fields (by either explicit or implicit redefinition) are not included by name, but are mapped to the key field column names by the XFD.
Remember, if the field named in the KEY IS phrase is a group item, it does not become a column in the database table unless a USE GROUP XFD directive is used (see the section How XFDs are Formed). Instead, the subordinate fields of the group item are used.