What is sequence in Oracle ?

What is purpose of sequence ?

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In oracle you can use sequence to generate primary key 

Syntax to create sequence

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CREATE SEQUENCE STUDENTS_ID_SEQ
    INCREMENT BY 1
    START WITH 1
    MAXVALUE 10000
    NOCACHE
    NOCYCLE;

Example:

create table students(
sid number primary key,
fname varchar2(100),
lname varchar2(100));

Insert statements 

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Insert into students values(STUDENTS_ID_SEQ.nextval,'Anil','kumar');
Insert into students values(STUDENTS_ID_SEQ.nextval,'Sunil','kumar');

Syntax to get the sequence number is sequencename.nextval. 

You can see that in the above insert statements

I call nextval to get the primary key which is automatically

generated by the sequence we created

When I created STUDENTS_ID_SEQ I said that sequence should start

with 1 and increment by 1 

So when u call the nextval for first time it generates 1

If you call again it will generate 2 

You can say increment as 2 

Then the generated sequences will be 1,3,5... 

If you don't know this.. you have to get the max student id and increment

it by one.... right ? 

To just display the next sequence number you can execute

following query 

select STUDENTS_ID_SEQ.nextval from dual; 

Small Task....... :)

Try to generate nextval more than 10000 times

and see what happens........ ?