A: Below we see a case where we set the row archival visibility parameter to "all"
thereby allowing us to see all of the rows that have been logically deleted:
alter session set row archival visibility = all;
We can then turn-on row invisibility back on by changing row archival visibility = "active":
alter session set row archival visibility = all;
B: To use ora_archive_state as an alternative to deleting rows, you need the following settings and parameters:
1.Create the table with the row archival clause
create table mytab (col1 number, col2 char(200)) row archival;
2.Now that the table is marked as row archival, you have two methods for removing rows, a permanent solution with the standard delete DML, plus the new syntax where you set ora_archive_state to a non-zero value:
update mytab set ora_archive_state=2 where col2='FRED';
3.To make "invisible rows" visible again, you simply set the rows ora_archive_state to zero:
update mytab set ora_archive_state=0 where col2='FRED';
Note:
* Starting in Oracle 12c, Oracle provides a new feature that allow you to "logically delete" a row in a table without physically removing the row. This effectively makes deleted rows "invisible" to all SQL and DML, but they can be revealed at any time, providing a sort of "instant" rollback method.
To use ora_archive_state as an alternative to deleting rows.

* You can create a password file using the password file creation utility, ORAPWD.
* Adding Users to a Password File
When you grant SYSDBA or SYSOPER privileges to a user, that user's name and privilege information are added to the password file. If the server does not have an EXCLUSIVE password file (that is, if the initialization parameter REMOTE_LOGIN_PASSWORDFILE is
NONE or SHARED, or the password file is missing), Oracle Database issues an error if you attempt to grant these privileges.
A user's name remains in the password file only as long as that user has at least one of these two privileges. If yourevoke both of these privileges, Oracle Database removes the user from the password file.
* The syntax of the ORAPWD command is as follows:
ORAPWD FILE=filename [ENTRIES=numusers]
[FORCE={Y|N}] [IGNORECASE={Y|N}] [NOSYSDBA={Y|N}]
* IGNORECASE
If thisargument is set to y, passwords are case-insensitive. That is, case is ignored when comparing the password that the user supplies during login with the password in the password file.

Explanation/Reference:
Explanation:
The most of the rows in SUBSCRIBE_LOG table are accessed once a week.