Which join is suitable for my Ajax data table in CI

Try this code, its should work.

function getdatatableajax()   {        if($this->input->get('search_term')) { $search_term = $this->input->get('search_term'); } else { $search_term = false;}       $this->load->library('datatables');       $this->datatables            ->select("sales.id as sid, sales.date as date, sales.reference_no as reference_no, sales.biller_name as biller_name, sales.customer_name as customer_name, sales.total_tax as total_tax, sales.total_tax2 as total_tax2, sales.total as total, internal_note as sintnote")            ->from('sales')            ->join(deliveries, 'sales.reference_no = deliveries.reference_no', 'left');            $this->datatables->add_column("Actions",             "<center><a href='#' title='$2' class='tip' data-html='true'><i class='icon-folder-close'></i></a> <a href='#' onClick=\"MyWindow=window.open('index.php?module=sales&view=view_invoice&id=$1', 'MyWindow','toolbar=0,location=0,directories=0,status=0,menubar=yes,scrollbars=yes,resizable=yes,width=1000,height=600'); return false;\" title='".$this->lang->line("view_invoice")."' class='tip'><i class='icon-fullscreen'></i></a>             <a href='index.php?module=sales&view=add_delivery&id=$1' title='".$this->lang->line("add_delivery_order")."' class='tip'><i class='icon-road'></i></a>            <a href='index.php?module=sales&view=pdf&id=$1' title='".$this->lang->line("download_pdf")."' class='tip'><i class='icon-file'></i></a>             <a href='index.php?module=sales&view=email_invoice&id=$1' title='".$this->lang->line("email_invoice")."' class='tip'><i class='icon-envelope'></i></a>            </center>", "sid, internal_note")        ->unset_column('sid')        ->unset_column('internal_note');       echo $this->datatables->generate();   }

The Ref Number is the Invoice number compare to the Sales table in generally. So try this code below and may it will furnish what you really want to populate from the DB.

   function getdatatableajax()   {        if($this->input->get('search_term')) { $search_term = $this->input->get('search_term'); } else { $search_term = false;}       $this->load->library('datatables');       $this->datatables            ->select("sales.id as sid, date, reference_no, biller_name, customer_name, total_tax, total_tax2, total, internal_note")            ->from('sales')            ->join(deliveries, 'sales.reference_no = deliveries.reference_no', 'left');            $this->datatables->add_column("Actions",             "<center><a href='#' title='$2' class='tip' data-html='true'><i class='icon-folder-close'></i></a> <a href='#' onClick=\"MyWindow=window.open('index.php?module=sales&view=view_invoice&id=$1', 'MyWindow','toolbar=0,location=0,directories=0,status=0,menubar=yes,scrollbars=yes,resizable=yes,width=1000,height=600'); return false;\" title='".$this->lang->line("view_invoice")."' class='tip'><i class='icon-fullscreen'></i></a>             <a href='index.php?module=sales&view=add_delivery&id=$1' title='".$this->lang->line("add_delivery_order")."' class='tip'><i class='icon-road'></i></a>            <a href='index.php?module=sales&view=pdf&id=$1' title='".$this->lang->line("download_pdf")."' class='tip'><i class='icon-file'></i></a>             <a href='index.php?module=sales&view=email_invoice&id=$1' title='".$this->lang->line("email_invoice")."' class='tip'><i class='icon-envelope'></i></a>            </center>", "sid, internal_note")        ->unset_column('sid')        ->unset_column('internal_note');       echo $this->datatables->generate();   }

This should do. It's a very crude form, but you get the idea.

//Select everything$this->db->select (  '*'  );//From sales$this->db->from ( 'sales as s' );//Where id of sales is equals to your id$this->ci->db->where ( 's.id', $id );//Join where id in sales is equals to id_sales in deliveries$this->ci->db->join (  'deliveries as d', 's.id = d.id_sale' );// Query$query = $this->ci->db->get (  );