ORA-18003: an outline already exists with this signature
Cause: The signature generation algorithm generates signatures that are are 16 bytes in length so it is highly unlikely that any 2 signatures will be identical. This message is raised in such a rare case.
Action: Either re-issue the statement that led to the outline being created with some whitespace added or force the outline to be created in a different category.
常见情况：如果用户尝试使用“CREATE OR REPLACE OUTLINE”命令更新现有的提纲，那么ORA-18003错误就会发生。
1.使用“DROP OUTLINE”命令删除现有提纲后
2.再次尝试执行“CREATE OR REPLACE OUTLINE”命令
3.如果仍然出现ORA-18003错误，则将“create_stored_outlines”参数改为“false”
4.尝试重启数据库实例，然后再次执行提纲创建命令