| ERROR | the materialized view does not have a UNION ALL marker column |
| CAUSE | For a materialized view with UNION ALL to be fast refreshable, it must have a UNION ALL marker column. This is a constant column, at the same ordinal position in each query block and must have distinct values in each query block. |
| ACTION | Add a UNION ALL marker column to each query block in the UNION ALL query defining the materialized view. |