Add a identity column in existing database

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PostgreSQL

Hi all

I have a table which contains around 7000+ data.

now i want to add a unique id column on the existing data and also later if user adds
any records, it should increment automatically.

e.g. Below is the existing data

1    name    54
1    name    50
2    age     88
3    place   12....

and i want like this

00001   1    name    54
00002   1    name    50
00003   2    age     88
00004   3    place   12....

Please tell me how to do this

I am sorry, i made a wrong tag.
I search in google and i got something called "serial" for auto-increment id which serves my purpose.

But one thing i want the number to start like this-"00000000001" and so on.