unable to fetch records from database

Hi
whats wrong in my following query. i got the error
Error Number: 1054
Unknown column 't.user_id' in 'where clause'
-------------------------my query------------

function ShowTransData($data){
$this->db->select('*')
->from('transaction')
->join('user', 'transaction.user_id = user.user_id')
->where('t.user_id='. $data);
$query = $this->db->get();
return $query->result();