文档课题：测试闪回查询与闪回版本.
应用场景：
a、恢复丢失的数据或撤消不正确的已提交的更改.如commit错误的dml事务，此时便可通过闪回查询将数据找回.
b、将当前数据与过去某一时刻的数据进行比较.
实际操作：
1、闪回查询
SQL> select employee_id,first_name,last_name,hire_date,salary from employees03;

EMPLOYEE_ID FIRST_NAME           LAST_NAME       HIRE_DATE                    SALARY
----------- -------------------- --------------- ----------------------------------- ----------
        100 Steven               King            17-JUN-11                                24000
        101 Neena                Kochhar         21-SEP-09                                17000
        102 Lex                  De Haan         13-JAN-09                                17000
        103 Alexander            Hunold          03-JAN-14                                 9000
        104 Bruce                Ernst           21-MAY-15                                 6000
        107 Diana                Lorentz         07-FEB-15                                 4200
        124 Kevin                Mourgos         16-NOV-15                                 5800
        141 Trenna               Rajs            17-OCT-11                                 3500
        142 Curtis               Davies          29-JAN-13                                 3100
        143 Randall              Matos           15-MAR-14                                 2600
        144 Peter                Vargas          09-JUL-14                                 2500

EMPLOYEE_ID FIRST_NAME           LAST_NAME       HIRE_DATE                    SALARY
----------- -------------------- --------------- ----------------------------------- ----------
        149 Eleni                Zlotkey         29-JAN-16                                10500
        174 Ellen                Abel            11-MAY-12                                11000
        176 Jonathon             Taylor          24-MAR-14                                 8600
        178 Kimberely            Grant           24-MAY-15                                 7000
        200 Jennifer             Whalen          17-SEP-11                                 4860
        201 Michael              Hartstein       17-FEB-12                                13000
        202 Pat                  Fay             17-AUG-13                                 6000
        205 Shelley              Higgins         07-JUN-10                                12008
        206 William              Gietz           07-JUN-10                                12008

20 rows selected.
SQL> select salary from employees03 where first_name='Kevin';                              

    SALARY
----------
      5800

SQL> update employees03 set salary=8500 where first_name='Kevin';

1 row updated.

SQL> commit;

Commit complete.

SQL> select salary from employees03 where first_name='Kevin';

    SALARY
----------
      8500

SQL> select salary from employees03 as of timestamp (systimestamp-interval '5' minute) where first_name='Kevin';

    SALARY
----------
      5800

SQL> select salary from employees03 as of timestamp (systimestamp-interval '1440' minute) where first_name='Kevin';

    SALARY
----------
      5800

说明：如上使用as of timestamp语句便可查出5分钟前或1天前的数据.
2、闪回版本查询
SQL> update employees03 set salary=9600 where first_name='Kevin';

1 row updated.

SQL> commit;

Commit complete.

SQL> select salary from employees03 versions between scn minvalue and maxvalue where first_name='Kevin';

    SALARY
----------
      9600
      8500

SQL> update employees03 set salary=salary*1.2 where first_name='Kevin';

1 row updated.

SQL> commit;

Commit complete.

SQL> select salary from employees03 versions between scn minvalue and maxvalue where first_name='Kevin';

    SALARY
----------
     11520
      9600
      8500
注意：执行过dml后需commit才能看到相应的修改记录.
SQL> select versions_starttime "START_DATE",versions_endtime "END_DATE",salary from employees03 versions between scn minvalue and maxvalue where first_name='Kevin'

START_DATE                END_DATE                      SALARY
------------------------- ------------------------- ----------
02-DEC-22 07.42.03 PM                                    11520
02-DEC-22 07.40.24 PM      02-DEC-22 07.42.03 PM           9600
                          02-DEC-22 07.40.24 PM           8500
说明：薪水11520对应版本END_DATE的NULL值表示目前查询的为现有版本.薪水8500对应版本START_DATE的NULL值表示该版本薪水超过undo retention保留时间.