$one_department_a = ORM::factory ('department', $id);

SELECT * FROM departments WHERE id=2 or id=(
SELECT main_dep_id FROM departments WHERE id=2)

$one_department_a = ORM::factory('department', $id)->as_array(); //получение инф-ции дной строки
$data['dep'] = ORM::factory('department', $data['main_dep_id'])->as_array(); //получение инф-ции связанной с первой строкой

$sub_sql = DB::select('main_dep_id')->from('departments')->where('id','=',$id);
$sub_sql1 = ORM::factory('department')->where('id','=',$id)->or_where('id','=', '('||DB::expr($sub_sql)||')')->find_all()->as_array();

SELECT `department`.`id` AS `id`, 
`department`.`name` AS `name`, 
`department`.`main_dep_id` AS `main_dep_id`, 
FROM `departments` AS `department` 
WHERE `id` = 24 OR `id` = (SELECT `main_dep_id` FROM `departments` WHERE `id` = 24)

$sub_sql = DB::select('main_dep_id')->from('departments')->where('id','=',$id)->execute()->as_array();

Array ( [0] => Array ( [main_dep_id] => 23 ) )

$sub_sql1 = ORM::factory('department')->where('id','=',$id)->or_where('id','=', '('||DB::expr($sub_sql)||')')->find_all()->as_array();

...FROM `departments` AS `department` WHERE `id` = 24 OR `id` = '1' 

$sub_sql4 = DB::query(Database::SELECT, 'SELECT id, abbreviation, name, main_dep_id, status, user_id, hierarchical_dep FROM departments WHERE id = :id OR id = (select main_dep_id from departments where id = :id)');
 $sub_sql4->param(':id', $id);
 $sub_sql4 = $sub_sql4->execute()->as_array()

...'('||DB::expr($sub_sql)||')'

...DB::expr('('.$sub_sql->compile().')')

foreach($one_department_a2 as $abbreviation)
{
    if ($abbreviation->id == $id)
    {    
    $one_department_a['dep']['id']  = $abbreviation->id;
    $one_department_a['dep']['abbreviation']  = $abbreviation->abbreviation;
    $one_department_a['dep']['name']  = $abbreviation->name;
    $one_department_a['dep']['main_dep_id']  = $abbreviation->main_dep_id;
    $one_department_a['dep']['status']  = $abbreviation->status;
    }
    else 
    {
     $one_department_a['mainDep']['id']  = $abbreviation->id;
     $one_department_a['mainDep']['abbreviation']  = $abbreviation->abbreviation;
     $one_department_a['mainDep']['name']  = $abbreviation->name;
     $one_department_a['mainDep']['main_dep_id']  = $abbreviation->main_dep_id;
     $one_department_a['mainDep']['status']  = $abbreviation->status;
    }    
    
}    

...
td width="100%"><?=Form::label('name', 'Полное название')?>:</td>
<td><?=Form::input('name', $one_department_a['dep']['name'], array('size' => 50))?></td>
...

...
<td><?=Form::label('name', 'Подчиненный отдел')?>:</td>
        <td>
            <?=Form::select('dep', $departments_a1, $one_department_a['mainDep']['id'], array('size' => 1))?><br/><br/>
        </td>
...

<?=Form::select('dep', $departments_a1, $one_department_a['mainDep']['id'], array('size' => 1))?><br/><br/>