SQL to function in Codeigniter returns row - php

Question

I'm trying to get an entire row values from a new SQL query so.
How can I make a function
Select * from table1 t1,table2 t2,table3 t3 where t1.t1_id=t2.t1_id and t3.id=t2.t3_id
to something like this :
In model page
public function getID_researcher($lastname){
$query = $this->db->get_where('researcher', array('lastname' => $lastname));
return $query->row_array();
}
I need to return one row result base on the lastname which is from table1
To clarify here, 'researcher' is the table where it gets data but what I want is the new SQL for me to get the data.
I tried this one but still error.
public function getID_researcher($lastname){
$sql = = $this->db->query('Select * from table1 t1,table2 t2,table3 t3 where t1.t1_id=t2.t1_id and t3.id=t2.t3_id');
$query = $this->db->get_where($sql, array('lastname' => $lastname));
return $query->row_array();
}

Answer 1

to use this query
Select * from table1 t1,table2 t2,table3 t3 where t1.t1_id=t2.t1_id and t3.id=t2.t3_id
you can try to use active record db 'join' like this:
$this->db->from('table1 t1');
$this->db->join('table2 t2', 't1.t1_id = t2.t1_id', 'left');
$this->db->join('table3 t3', 't3.id = t2.t3_id', 'left');
$this->db->where('lastname', $lastname);
$query = $this->db->get();
$c = 0;
foreach($query->result() as $q){
$result[$c]['name'] = $q->lastname;
// put move variable here
$c++;
}
return $result;
hope this help