Join two tables with two or three same field

[eluser]Anil3a[/eluser]
I am newbie so bear with me. I was trying to join two tables having

Code:

gift_id = transact.id, item_id=item_id and user_id=user_id

Should i code like

Code:

$this->db->select('*');
$this->db->from('gift');

$this->db->join('transact', 'transact.id=gift.gift_id,transact.item_id=gift.item_id, transact.user_id=gift.user_id');

$query = $this->db->get();
return $query->result();

And What is really the Left join does ?