In a Report of more than 1 page information. Then BETWEEN
PAGES trigger fire when one move from one page to other
page. In this trigger we can write process which is required
to affect other page values.

retrieving 8th record from emp table in scott instance

select * from emp where rownum<=8
minus
select * from emp where rownum<=7

Introduction to Oracle 9i: OCA/OCP
- Biju Thomas/Chip Dawes

Refer this for concise coverage of topics as per the 
importance.

Implicit : Every SQL Statement performed as implicit cursor. Ex: Select * from Emp where empno = 7839 This is query automatically open the cursor and fetch the record getting the output of that record.

Explicit : In PLSql Block in we declare on declaration section we declare with name and select statement. In executable block we call the cursor and fetch the records more the one. For Ex : Declare
cursor c1 is select * from emp
getemp c1%rowtype;
begin
open c1;
loop
fetch c1 into getemp;
dbms_output.put_line (c1.col list);
end loop;
close c1;
end;  This is explicit cursor

delete from abc where rowid not in (select max(rowid) from
abc group by column_name_with_dup.values.);

delete from emp e1 where rowid >(select min(rowid) from emp 
e2 where e1.empid=e2.empid)

delete from 
<<table_name>>
where rowid in 
(select a.rowid
from <<table_name a,table_name b>>
where a.colname = b.colname
b.colname2 = b.colname2
......
...
a.colnamen = colnamen
order by .... desired colnames)

Primary key and unique are Entity integrity constraints

Primary key allows each row in a table to be uniquely 
identified and ensures that no duplicate rows exist and no 
null values are entered.

Unique key constraint is used to prevent the duplication of 
key values within the rows of a table and allow null 
values. (In oracle, one null is not equal to another null).

More or less both the keys sounds same, but the major 
diffrence is where unique will allow null values, because 
each null treated as a diffrent value internally. Incase of 
primary key it will not allow any repeated data and null 
data.

Yes.When a column is assigned primary key it means it 
contains unique value(i.e. no duplicate value is allowed) & 
it can't accept null values.
  Whereas unique key means no duplicare value is allowed, but
null value is allowed. And not null means no null value is
accepted but duplicate value can be passed.
 So when we assign primary key to a column, the column
becomes both unique & not null.

oracle 10g has introduced data pump,awr addm etc

oracle 10g has many features compare to 9i like
asm,swr,addm,flaskback recovery,data pump..
generating snap shot is much more flxible in 10 g compare to 9i

Plese see thin link: http://www.orafaq.com/wiki/PL/SQL_FAQ