Note the following statements that use flashback technology:
1. FLASHBACK TABLE <table> TO SCN <scn>;
2. SELECT * FROM <table> AS OF SCN 123456;
3. FLASHBACK TABLE <table> TO BEFORE DROP;
4. FLASHBACK DATABASE TO TIMESTAMP <timestamp>;
5. SELECT * FROM <table> VERSIONS AS OF SCN 123456 AND 123999;
Which of these statements will be dependent on the availability of relevant undo data in the undo
segment?
A. 1, 2, and 5
B. 1, 3, and 4
C. 2, 3, 4, and 5
D. 1, 2, 3, 4, and 5
1.闪回表原理是还原数据。
2.闪回查询是还原数据。
3.闪回删除是回收站原理。
4.闪回数据库是基于闪回日志。
5.闪回版本查询是基于还原数据。
所以基于还原数据的是 125.
原文：http://www.cnblogs.com/Babylon/p/7843564.html