數據庫中閃回有哪些

小編給大家分享一下數據庫中閃回有哪些，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！

閃回主要有閃回表、閃回查詢、閃回數據庫(數據來自閃回日志)三種，這里主要了解閃回表和閃回查詢

閃回表：又分以下2種：
Flashback table tablename to before drop(數據來自回收站)
Flashback table tablename to scn/timestamp(數據來自UNDO，必須開啟Row movement)

閃回查詢：又分以下3種
閃回查詢AS OF SCN/TIMESTAMP(數據來自UNDO)
閃回版本查詢Flashback Version Query(數據來自UNDO)
閃回事務查詢Flashback Transaction Query(數據來自UNDO)


閃回表中關于Row movement和Recyclebin的知識點
The row_movement_clause lets you specify whether the database can move a table row. Specify ENABLE to allow the database to move a row, thus changing the rowid.
Row movement must be enabled for all tables in the Flashback list unless you are flashing back the table TO BEFORE DROP. That operation is called a flashback drop operation, and it uses dropped data in the recycle bin rather than undo data.
row_movement_clause允許您指定數據庫是否可以移動表行。指定ENABLE以允許數據庫移動一行，從而更改rowid。
閃回必須開啟行移動，但是閃回DROP不需要開啟Row movement，且數據來自回收站

Flashback table后不需要提交，直接就自動提交了
Flashback table user_tables.TABLE_NAME to before drop(user_tables.TABLE_NAME就是recyclebin.ORIGINAL_NAME)
Flashback table recyclebin.OBJECT_NAME to before drop(當一個table刪除兩次時，可以指定回收站里名稱按順序指定回收哪次刪除的表)
Flashback table TABLE_NAME to before drop rename to TABLE_NAME2(當刪除一個表后，又建立了一張同名表時，可以使用rename to恢復成其他名稱的表)
Purge recyclebin只是清空當前用戶的回收站
Purge dba_recyclebin清空所有用戶的回收站







閃回表、閃回查詢的一個示例
SQL> create table hr.test1(id number primary key,name varchar2(10));
Table created.

SQL> begin
  2      insert into test1 values(1,'A');
  3      insert into test1 values(2,'B');
  4      insert into test1 values(3,'C');
  5      commit;
  6      dbms_lock.sleep(5);
  7      update test1 set name='C-1' where id=3;
  8      insert into test1 values(4,'D');
  9      commit;
 10      end;
 11     /
PL/SQL procedure successfully completed.

--閃回版本查詢
SQL> select versions_startscn,versions_endscn,versions_xid,versions_operation,name from test1 versions BETWEEN SCN MINVALUE AND MAXVALUE;
VERSIONS_STARTSCN VERSIONS_ENDSCN VERSIONS_XID     VE NAME
----------------- --------------- ---------------- -- --------------------
          4083242                 03002000610D0000 I  D
          4083242                 03002000610D0000 U  C-1
          4083235         4083242 01000400970C0000 I  C
          4083235                 01000400970C0000 I  B
          4083235                 01000400970C0000 I  A

--閃回查詢AS OF SCN
SQL> select * from test1 as of scn 4083235;
        ID NAME
---------- --------------------
         1 A
         2 B
         3 C

--閃回版本查詢
SQL> select versions_startscn,versions_endscn,versions_xid,versions_operation,name from test1 versions BETWEEN TIMESTAMP TO_TIMESTAMP('2017-08-16 14:17:10','YYYY-MM-DD HH24:MI:SS')  AND TO_TIMESTAMP('2017-08-16 14:19:26','YYYY-MM-DD HH24:MI:SS');
VERSIONS_STARTSCN VERSIONS_ENDSCN VERSIONS_XID     VE NAME
----------------- --------------- ---------------- -- --------------------
          4083242                 03002000610D0000 I  D
          4083242                 03002000610D0000 U  C-1
          4083235         4083242 01000400970C0000 I  C
          4083235                 01000400970C0000 I  B
          4083235                 01000400970C0000 I  A

--閃回查詢AS OF TIMESTAMP
SQL> select * from test1 AS OF TIMESTAMP TO_TIMESTAMP('2017-08-16 14:17:16','YYYY-MM-DD HH24:MI:SS');
        ID NAME
---------- --------------------
         1 A
         2 B
         3 C

--閃回事務查詢
SQL> SELECT undo_sql FROM flashback_transaction_query WHERE xid = HEXTORAW('03002000610D0000');
UNDO_SQL
--------------------------------------------------------------------------------
delete from "HR"."TEST1" where ROWID = 'AAAWV2AAEAAAAJXAAD';
update "HR"."TEST1" set "NAME" = 'C' where ROWID = 'AAAWV2AAEAAAAJXAAC';

SQL> select * from test1;
        ID NAME
---------- --------------------
         1 A
         2 B
         3 C-1
         4 D

--啟用ROW MOVEMENT
SQL> ALTER TABLE test1 ENABLE ROW MOVEMENT;
Table altered.

--Flashback table to SCN
SQL> flashback table test1 to scn 4083235;
Flashback complete.

SQL> select * from test1;
        ID NAME
---------- --------------------
         1 A
         2 B
         3 C

SQL> drop table test1;
Table dropped.

--Flashback table to BEFORE DROP
SQL> FLASHBACK TABLE test1 TO BEFORE DROP;
Flashback complete.

SQL> drop table test1;
Table dropped.

--Flashback table to BEFORE DROP RENAME
SQL> FLASHBACK TABLE test1 TO BEFORE DROP RENAME TO test1_2017;
Flashback complete.

SQL> select * from test1_2017;
        ID NAME
---------- --------------------
         1 A
         2 B
         3 C

以上是“數據庫中閃回有哪些”這篇文章的所有內容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內容對大家有所幫助，如果還想學習更多知識，歡迎關注億速云行業資訊頻道！