How do i manipulate third uri segment ?

[eluser]dhaulagiri[/eluser]
I thought 3rd segment of the URI directly corresponds to database id, as i assume, what it happens in other application.

for example I have 25 rows of data in a table, I want to point that database id in a url and fetch all the data on the corresponding fields of the 'id'.

how do i assign id in such scene?
I have seen example somewhere $this->uri->segment(3) = $id . How will this work with my database ? Sorry I am realtively new.

[eluser]Krzemo[/eluser]
Its all written here:
URI Class : CodeIgniter User Guide

Usually first segment is controller class, second is its function and 3rd and the rest are parameters you want to pass to it - and as those they can be used almost and as for whatever you want.