Oracle Solution for Error ora-29921

ORA-29921: Ancillary operator not supported with set view query block

What triggered the Error:

Outer view query block contains ancillary operator and view query block contains union all.

What should we do to fix it:

Define the union-all view query to contain the primary and ancillary query terms. i.e. have the operators within the view definition rather than in the query outside the view.