Get multiple taxonomies in the same node on DBSELECT

Hello,

I try to get a list of nodes with multiple taxonomies inside. So I create a dbselect like this : 

$select = db_select('node', 'n');
$select->fields('n', array('nid', 'title'));
$select->condition('n.type', 'mycontentype');
$select->condition('n.status', 1);
$select->leftjoin('field_data_field_mytaxonomies', 't', 't.entity_id = n.nid');
$select->fields('t', array('field_mytaxonomies_tid'));
$select->orderBy('n.created', 'ASC');
$nodes = $select->execute()->fetchAll();
return $nodes;

But with this i’ve one result for one taxonomy saved in the same node. Like this :

Array ( 
  [0] => stdClass Object ( 
    [field_mytaxonomies_tid] => 1 
    [nid] => 1 
    [title] => 'My first node'
  ) 
  [1] => stdClass Object ( 
    [field_mytaxonomies_tid] => 2 
    [nid] => 1 
    [title] => 'My first node'
  ) 
  [2] => stdClass Object ( 
    [field_mytaxonomies_tid] => 3 
    [nid] => 1 
    [title] => 'My first node'
  ) 
  [3] => stdClass Object ( 
    [field_mytaxonomies_tid] => 1 
    [nid] => 2 
    [title] => 'My second node'
  ) 
  [4] => stdClass Object ( 
    [field_mytaxonomies_tid] => 3 
    [nid] => 2 
    [title] => 'My second node'
  ) 
)

But i want to have, one result for one node with multiple taxonomies inside, like this :

Array ( 
  [0] => stdClass Object ( 
    [field_mytaxonomies_tid] => 1,2,3 
    [nid] => 1 
    [title] => 'My first node'
  ) 
  [1] => stdClass Object ( 
    [field_mytaxonomies_tid] => 1,3
    [nid] => 2
    [title] => 'My second node'
  ) 
)

Have you got an idea to do this ?

Thanks for your help !

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/4/feed