There are no foreign keys available to use for subsetting. This can be as a result of their being no foreign keys defined in the database, or all of the defined foreign keys have been excluded as a result of excluding the tables that they are defined on.

Subsetting relies on foreign key relationships to work out how to traverse a database's schema so that it can subset correctly. With no foreign keys, the resulting subset would contain only the data from one table. It is possible to subset a database that has no foreign keys by defining manual relationships via an options file.

How to fix

Configure manual relationships in the options file representing any relationships between tables that are not defined by foreign keys in the database itself.