Asking about performance of data retrieval

[eluser]dimazarno[/eluser]
hello,

i write code like this, i'm using variable $type for select and return value from single field, whether this will affects the performance of data retrieval?

Code:

//get one field value
    function get_shop($type){
        $this->db->select($type);
        $this->db->from('shop');
        $query = $this->db->get();    
        foreach ($query->result() as $row)
        {
            return $row->$type;
        }        
    }

thanks.