回收站里的对象：
SQL> purge recyclebin;
回收站已清空。
SQL> select tname from tab
2where tname like 'BIN%';
未选定行
SQL> drop table dept;
表已删除。
SQL> select tname from tab
2where tname like 'BIN%';
TNAME
------------------------------
BIN$ev3TI+yATu+U8xlA49LMfg==$0
SQL> flashback table dept to before drop;
闪回完成。
SQL> select tname from tab
2where tname like 'BIN%';
未选定行
SQL> select * from dept;
DEPTNO DNAME
LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES
CHICAGO
40 OPERATIONS BOSTON
50 ADMIN
BEIJING
