今天写了一个存储过程，需要通过dblink把其他用户下面的表的数据增量copy到目标表中，结果访问其他系统的表的时候，在存储过程中一直有问题，在Stack Overflow中找到了答案。

In stored procedures, functions, and definers-rights packages, roles (such as  SELECT_CATALOG_ROLE ) are disabled. Therefore,  such a PL/SQL program can only fetch metadata for objects in its own schema . If you want to write a PL/SQL program that fetches metadata for objects in a different schema (based on the invoker's possession of SELECT_CATALOG_ROLE ), you must make the program invokers-rights.

To do this, you must add  authid  to your procedure.

create procedure tests authid CURRENT_USER is
  l_foo clob;beginselectregexp_replace(
  dbms_metadata.get_ddl('USER', 'SCOTT', null) ||
  dbms_metadata.GET_GRANTED_DDL ('SYSTEM_GRANT', 'SCOTT') ||
  dbms_metadata.GET_GRANTED_DDL ('OBJECT_GRANT', 'SCOTT') ||
  dbms_metadata.GET_GRANTED_DDL ('ROLE_GRANT', 'SCOTT'),'"' || chr(10), '";' || chr(10)) into l_foo 
from dual;end;/SQL> EXEC tests 
PL/SQL procedure successfully completed