Primary key,Froign key , Unique key

Question

I want the answer of following questions.
1) Primary key create cluster index or simple index?
2) What is cluster index : I know only( cluster index stored record at physical level in sorted order) if there is another difference then tell me
3) Can I set relation ship with unique key if it is specified with NOT NULL constraints in a table.
4) Foreign key creates a index or not?

Answer 1

Hello
I want to be at least 6 inches taller, better looking and really good at playing the drums, but that's neither here nor there.
A simple please never hurts.
For answers to the first 2 I'd concentrate on the clusters section of the concepts guide as your understanding of what clusters are for and when they should be used appears to be lacking:
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96524/c11schem.htm#25479
and also have a look at this asktom thread:
http://asktom.oracle.com/pls/ask/f?p=4950:8:6996872588440689863::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:1308402202736
The last two questions, again you can find the info you need in the concepts guide but
3) Can I set relation ship with unique key if it is specified with NOT NULL constraints in a table.To set up a foreign key from one table to another, it needs to reference a primary key or a unique key in the target table, the NOT NULL constraint has very little to do with it. A very simple test will show this:
SQL> create table dt_test(id number);
Table created.
SQL> create table dt_test_fk(id number);
Table created.
SQL> create table dt_test_fk(id number, pk_id number);
Table created.
SQL> alter table dt_test_fk add constraint fk_dt_test_fk FOREIGN KEY(pk_id) references dt_test(id);
alter table dt_test_fk add constraint fk_dt_test_fk FOREIGN KEY(pk_id) references dt_test(id)
ERROR at line 1:
ORA-02270: no matching unique or primary key for this column-list
SQL> alter table dt_test add constraint uk_dt_test UNIQUE (id);
Table altered.
SQL> alter table dt_test_fk add constraint fk_dt_test_fk FOREIGN KEY(pk_id) references dt_test(id);
Table altered.
SQL> alter table dt_test modify(id number not null);
Table altered.
4) Foreign key creates a index or not? Creating a foreign key on a column does NOT automatically create an index on that column.
A primary key may create a new index. If an index is already available on the table and it can be used i.e the leading edge of the index holds the columns in the primary key, it will be used rather than creating a new one.
HTH