CREATE [ OR REPLACE ] TRIGGER [ schema. ]trigger
   { BEFORE | AFTER | INSTEAD OF }
   { DELETE | INSERT | UPDATE 
     [ OF column [, column ]... ]
}
  [ OR { DELETE | INSERT | UPDATE 
       [ OF column [, column]... ]
       }
  ]...
ON { [ schema. ]table
      }
[ FOR EACH ROW ]
     ON { [ schema. ]SCHEMA 
           }
   }
   [ WHEN (condition) ]
   { pl/sql_block } ;

SQL> CREATE OR REPLACE TRIGGER Log_emp
  2    BEFORE INSERT OR DELETE OR UPDATE ON emp
  3    FOR EACH ROW
  4  BEGIN
  5    IF INSERTING THEN
  6      DBMS_OUTPUT.put_line('Insert on emp ' ||' '|| USER ||' ' ||SYSDATE);
  7    ELSIF UPDATING THEN
  8      DBMS_OUTPUT.put_line('Update on emp ' ||' '|| USER ||' ' ||SYSDATE);
  9    ELSIF DELETING THEN
 10      DBMS_OUTPUT.put_line('Delete on emp ' ||' '|| USER ||' ' ||SYSDATE);
 11    END IF;
 12  END;