Oracle Error Message
QSM-01125: a more optimal set operator materialized view than string was used to rewrite
Reason for the Error
Query Rewrite always chooses the most optimal set operator materialized view based on parameters, such as cardinality of the set operator materialized view, number of branches that the set operator materialized view can rewrite etc. The set operator materialized view specified was found to be less optimal.
Solution
To force using a set operator materialized view, consider using a rewrite hint.
