Overview of Joined Columns
A joined column is a column whose values a database object "borrows" from its parent object. Such a column is borrowed in the sense that the column is not part of the child object proper. "Joined columns" are therefore also referred to as "virtual columns" (as opposed to "database columns").
Because database objects may be related in more than one way, you must define the joined column using the specific relationship involved, i.e. the role defined for the parent-child relationship between the two database objects For more information on relationships, see "Overview of Relationships".
You can also have an object borrow values from a parent, which itself has borrowed the values from a grandparent. In this way it is possible to create joined columns over parents, grandparents, great-grandparents, etc. Performance may be adversely affected, however, because of the time needed to query the database.
Joined columns MUST be based on the same domain as the parent column they take their values from.
Joined columns, whether specified in the Definer or inserted via the Windows Designer, cannot be accessed by means of ODBC.
Joined columns cannot retrieve values from the supertype of the parent in a relationship. The workaround is to define Extra Query columns, as described in the USoft Windows Designer Help.