Auto-Increment in Postgres

Dear all,

I have an Integer column in Postgres database table. Let's say the
column has below values :

1
2
3
4
5
6
7
8
9
10

Now if i deleted some rows where id= 3 ,5 and 8 or it have these type
of data then

The data look like as :

1
2
4
6
7
9
10

I want to have it id's as
1
2
3
4
5
6
7
and next data is inserted right at 8 .

I follow these steps

*alter table meta_test drop column metadataid;

alter table meta_test add metadataid serial;*

But this adds the column at the end but i want to it as primary key.

Please help how to achieve it.

Thanks & best Regards
Adarsh Sharma