Selecting from database based on another query

What I am trying to do is search my privileges table where db_id column holds which database a user has rights to.  From that database I want to pull all the user_id that have a db_id... ie: 2.

I then want to search my user table for those user_id and list all of their details.

The problem I can not solve is getting the array of user_ids in where where statement.
Please see the included code.  Any advice would be greatly appreciated.

Code:

function return_users(){
            
                $this->db_core->where('db_id', $this->session->userdata("db_id"));
                $this->db_core->select('user_id');
                $query = $this->db_core->get('privileges');
    
                
                foreach($query->result() as $row) {
                    $priv[] = $row->user_id;
                    };

                $this->db_core->where('user_id', $priv);
                $list_users = $this->db_core->get('users');
                $list_users->result_array();
                
                return $list_users->result();
        }