drop后的表被放在回收站(user_recyclebin)里，而不是直接删除掉。这样，回收站里的表信息就可以被恢复，或彻底清除。 
1.通过查询回收站user_recyclebin获取被删除的表信息，然后使用语句
flashback table <user_recyclebin.object_name or user_recyclebin.original_name> to before drop [rename to <new_table_name>];

将回收站里的表恢复为原名称或指定新名称，表中数据不会丢失。
若要彻底删除表，则使用语句：drop table <table_name> purge;

2.清除回收站里的信息
清除指定表：purge table <table_name>;
清除当前用户的回收站：purge recyclebin;
清除所有用户的回收站：purge dba_recyclebin;

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Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 
Connected as test
SQL> select * from test1;
A B C
-- -- ----------
11 5 
11 10 
11 10 
13 10 
14 10 
15 10 
16 10 
17 10 
18 10 
19 10 
20 11 
11 rows selected
SQL> create table test2 as select * from test1;s
Table created
SQL> select * from test2;
A B C
-- -- ----------
11 5 
11 10 
11 10 
13 10 
14 10 
15 10 
16 10 
17 10 
18 10 
19 10 
20 11 
11 rows selected
SQL> drop table test2;
Table dropped
SQL> select object_name, original_name, operation, type from user_recyclebin;
OBJECT_NAME ORIGINAL_NAME OPERATION TYPE
------------------------------ -------------------------------- --------- -------------------------
BIN$g5jFmA/OShC6+wsWKJiv2w==$0 TEST1 DROP TABLE
BIN$vQwemDg4R9mK9fYJNdYzvg==$0 TEST2 DROP TABLE
SQL> flashback table test2 to before drop rename to test3;--【to test3】将表重命名
Done
SQL> select * from test3;
A B C
-- -- ----------
11 5 
11 10 
11 10 
13 10 
14 10 
15 10 
16 10 
17 10 
18 10 
19 10 
20 11 
11 rows selected
SQL> select * from test2;
select * from test2
ORA-00942: 表或视图不存在
--彻底删除表
SQL> drop table test3 purge;
Table dropped
SQL> select * from user_recyclebin where original_name = ‘TEST3‘;
OBJECT_NAME ORIGINAL_NAME OPERATION TYPE TS_NAME CREATETIME DROPTIME DROPSCN PARTITION_NAME CAN_UNDROP CAN_PURGE RELATED BASE_OBJECT PURGE_OBJECT SPACE
------------------------------ -------------------------------- --------- ------------------------- ------------------------------ ------------------- ------------------- ------- -------------------------------- ---------- --------- ------- ----------- ------------ -----
SQL> select * from user_recyclebin;
OBJECT_NAME ORIGINAL_NAME OPERATION TYPE TS_NAME CREATETIME DROPTIME DROPSCN PARTITION_NAME CAN_UNDROP CAN_PURGE RELATED BASE_OBJECT PURGE_OBJECT SPACE
------------------------------ -------------------------------- --------- ------------------------- ------------------------------ ------------------- ------------------- ------- -------------------------------- ---------- --------- ------- ----------- ------------ -----
BIN$g5jFmA/OShC6+wsWKJiv2w==$0 TEST1 DROP TABLE TP_TEST1 2007-08-23:07:57:28 2007-08-23:07:58:51 1411156 YES YES 53086 53086 53086 896
--清除回收站里的表信息test1
SQL> purge table test1;
Done
SQL> select * From user_recyclebin;
OBJECT_NAME ORIGINAL_NAME OPERATION TYPE TS_NAME CREATETIME DROPTIME DROPSCN PARTITION_NAME CAN_UNDROP CAN_PURGE RELATED BASE_OBJECT PURGE_OBJECT SPACE