When To Use A RowID

I have complied while doing my oracle stuff.

1. When do you use a rowID?
2. if you have this:

alter table shopowner.jobs
add constraint uk_salary
unique (min_salary, max_salary);
insert into shopowner.jobs
values (3, 'dba', 20002,55000, 'jobs');

Why does the above constraint not fail when one of these columns are not unique? It needs to fail both to fail the constraint.

3. what is a transaction? and how do you do it? how does deferred transaction look like?

4. How do you view constraints through isqlplus?
5. How do you drop multiple constraints at once?
6. When would you not use cascading delete?
7. How do you use create like cmd in enterprise Manger? I keep getting this error Failed to

commit: ORA-02264: name already used by an existing constraint even if you delete every constraint or rename ever constraint to anything.

8. how to make comments in isqlplus?
9. how do you add multiple insert values in at once in isqlplus?