ORA-23417: unknown materialized view type: string
Cause: A fast refresh is being performed on a materialized view of an unknown or unsupported type.
Action: Check all_mviews and ensure that the materialized view being refreshed a valid materialized view.
ORA-23417: unknown materialized view type: string是Oracle数据库给出的一条错误信息，表示用户向数据库服务器发出的命令中包含有无法识别的视图类型字符串。这个错误信息表明，ORACLE不支持用户请求的视图类型。