文档解释
ORA-32303: mviews with user-defined types cannot reference multiple master sites
Cause: For materialized views with user-defined types, the definition query cannot reference tables from different master sites.
Action: Do not create materialized views with user-defined types referencing multiple master sites.
ORA-32303: mviews with user-defined types cannot reference multiple master sites是Oracle数据库在执行Materialized View(MV)语句时报出的异常错误，是由于MV语句包含有ORACLE包以及用户自定义的数据类型。而ORACLE数据库规则只允许MV语句只能引用一个主站（master site），不能引用多个主站实现同步操作。
官方解释
ORA-32303: materialized views with user-defined types cannot reference multiple master sites
Cause: Oracle requires that materialized view definitions that use user-defined type references should be based on a single master site. All user-defined type references must be resolved with the maximum source of authority, which is in the master site.
Action: Rewrite the MV definition such that it does not reference more than one master site.
常见案例
Oracle提供的user-defined types，包括用于控制标签(Tags)和列类型，以及用于管理接口和类型(Types)。当使用这些user-defined types引用MV时，ORACLE数据库会引发ORA-32303异常错误。
一般处理方法及步骤
1. 确认MV语句是否正确，去除引用了多个主站的用户自定义类型。
2. 确认MV语句是否合法，检查语句是否符合ORACLE标准以及PSR标准；
3. 重写MV语句，将user-defined types合并或拆分成只引用一个主站；
4. 根据分析建议，确定重写后MV语句是否如预期，正确无误；
5. 执行重写后的MV语句，及检查MV结果是否正确；
6. 在对应的主站完成同步操作，完成MV的创建。
