CREATE TRIGGER on DB

trigger_definition
    :    CREATE [OR REPLACE] TRIGGER [IF NOT EXISTS] trigger_name
         trigger_action_time
         {    trigger_dml_event_clause 
         |    trigger_db_event_clause 
         |    trigger_ddl_event_clause 
         }
         compound_statement

trigger_action_time
    :    { BEFORE | AFTER } 

trigger_db_event_clause
    :    { LOGON | LOGOFF | STARTUP | SHUTDOWN }