package User;
# read the docs for why not to sub-class exactly like this
use base Class::DBI::mysql; 

__PACKAGE__->set_db('Main', 'dbi:mysql:dbname', 'user', 'password');

__PACKAGE__->set_up_table( 'USERINFORMATION');

1;

# In your program
package main;

use User;

my $howmany = User->count;

my $user = User->search(username => $_[0]);
print $user->userid;
print $user->username;

#update username
$user->username('Biff');
$user->update;