通过Oracle10g的flashback transaction query新特性进行事务撤销

具备了flashback version query查询的基础，我们就可以进行基于flashback version query的恢复.

这就是flashback transaction query。flashback transaction query可以从FLASHBACK_TRANSACTION_QUERY中获得指定事务的历史信息以及Undo_SQL，通过这个UNDO_SQL，我们就可以恢复特定的事务。

Flashback transaction query需要用到FLASHBACK_TRANSACTION_QUERY视图，我们先看一下视图

SQL> desc FLASHBACK_TRANSACTION_QUERY;
Name             Type           Nullable Default Comments                
---------------- -------------- -------- ------- -------------------------- 
XID              RAW(8)          Y       Transaction identifier   
START_SCN        NUMBER          Y       Transaction start SCN    
START_TIMESTAMP  DATE            Y       Transaction start timestamp   
COMMIT_SCN       NUMBER          Y       Transaction commit SCN  
COMMIT_TIMESTAMP DATE            Y       Transaction commit timestamp  
LOGON_USER       VARCHAR2(30)    Y       Logon user for transaction   
UNDO_CHANGE#     NUMBER          Y       1-based undo change number  
OPERATION        VARCHAR2(32)    Y       forward operation for this undo  
TABLE_NAME       VARCHAR2(256)   Y       table name to which this undo applies     
TABLE_OWNER      VARCHAR2(32)    Y       owner of table to which this undo applies
ROW_ID           VARCHAR2(19)    Y       rowid to which this undo applies          
UNDO_SQL         VARCHAR2(4000)  Y       SQL corresponding to this undo