generated column is a special column which is always computed from other columns.
attgenerated has been added to pg_attribute to indicate whether the column is generated;
s indicates the column is of type
STORED, otherwise the value is empty and the column is not a generated one.
Foreign data wrapper (FDW) support
Foreign tables can be defined with generated columns, and the generated value will be supplied to the underlying foreign data wrapper. The FDW should ensure the value is stored on the foreign server and that it can be subsequently retrieved, however there is no guarantee that the retrieved value will not have been changed on the foreign server.