generating unique account ID -- Drupal 7

account_id.install

<?php

/**
* implements hook_schema()
*/

function cribs_schema()
{
    $schema['cribs'] = array(
      'description' => 'table holding account id of users',
      'fields' => array(
        'uid' => array(
          'description' => 'user id from users table',
          'type' => 'int',
          'not null' => TRUE,
        ),
        'accountid' => array(
          'description' => 'variable generated from cribs module',
          'type' => 'varchar',
          'length' => '256',
          'not null' => TRUE,
        ),
       ),
        'foreign keys' => array(
           'user_account' => array(
           'table' => 'users',
           'columns' => array('uid' => 'uid'),
            ),
         ),
      'indexes' => array(
        'uid' => array('uid'),
      ),
    );
    return $schema;
}

account_id.module

function cribs_user_insert(&$edit, $account, $category) {
kpr($edit);
kpr($account);
    function _cribs_accountid_during($account){
        $strip = substr($account->name, 0, -2);
        $content = $strip . '490' . $account->uid;
        return $content;
    }
    //insert records into database
    db_insert('cribs')
        ->fields( array(
            'uid'=> $account->uid,
            'accountid'=> _cribs_accountid_during($account),
        ))
        ->execute();
}