Join query of two databases in codeigniter

Question

I need to write a join query of two tables from two databases and fetch the joined data. For eg, consider I have a database db1 which has some tables named companies, plans, customers. Suppose I need to join the two tables companies and plans with another table 'cdr' on another database db2 by grouping them using a similar column.

The query which I'm running right now is given below:

function get_per_company_total_use ($custid)
        {         
                 $this->DB1->select('ph_Companies.CompanyName');
                 $this->DB1->where('ph_Companies.Cust_ID', $custid);
                 $this->DB2->select_sum('cdr.call_length_billable')->from('cdr');
                 $this->DB2->group_by('cdr.CompanyName');
                 $this->db->join('Kalix2.ph_Companies', 'Kalix2.ph_Companies.CompanyName = Asterisk.cdr.CompanyName');
                 $query = $this->db->get();
                 if($query->result()){
                     foreach ($query->result() as $value) {
                         $companies[]= array($value->CompanyName,$value->call_length_billable);
                          }
                     return $companies;
                 }
                 else 
                     return FALSE;
        }

But my query is not fetching the data and throwing an error. This same query, I have run on a single database and is working. But I need help to find how this can be done with two databases.

Solution

You can just give the following if you need to join two database tables:

function get_per_company_total_use ($custid)
        {         
                 $this->db->select('Kalix2.ph_Companies.CompanyName');
                 $this->db->where('Kalix2.ph_Companies.Cust_ID', $custid);
                 $this->db->select_sum('Asterisk.cdr.call_length_billable')->from('Asterisk.cdr');
                 $this->db->group_by('Asterisk.cdr.CompanyName');
                 $this->db->join('Kalix2.ph_Companies', 'Kalix2.ph_Companies.CompanyName = Asterisk.cdr.CompanyName');
                 $query = $this->db->get();
                 if($query->result()){
                     foreach ($query->result() as $value) {
                         $companies[]= array($value->CompanyName,$value->call_length_billable);
                          }
                     return $companies;
                 }
                 else 
                     return FALSE;
        }

Here actually you need not give the connection variable DB1 or DB2, just give $this->db.