调试Oracle DDL触发器

Question

无法理解为什么Oracle没有发射任何DDL触发器。

>SELECT * FROM V$VERSION 
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production

示例来自 https://docs.oracle.com/en/database/oracle/oracle-database/21/lnpls/plsql-triggers.html-trigggers.html#guid-6cf3a208-08-0be7-0be7-0be7-0be7-0be7-45ff-928f-928f-928c-a75555555555555555555555555555550

STUDENT> CREATE OR REPLACE TRIGGER drop_trigger
           BEFORE DROP ON student.SCHEMA
           BEGIN
             RAISE_APPLICATION_ERROR (
               num => -20000,
               msg => 'Cannot drop object');
           END;
[2022-04-29 11:28:09] completed in 293 ms
STUDENT> create table  tbl1 (a integer)
[2022-04-29 11:28:16] completed in 124 ms
STUDENT> drop table tbl1
[2022-04-29 11:28:17] completed in 155 ms

用户和模式 - 两个“学生”；

与DDL-Logging示例完全相同，来自

after ddl on schema 
after ddl on student.schema 
after ddl on database   -- created from name of SYS user

​ user_errors或all_errors没有与问题相关的消息

吗？