Codeigniter Database Joins two columns based on multiple values

I want to help with the following query: -

    $this->db->select('nbr.*, dm.dma, st.abbrev as state,unit.size_title as ad_size_title,unit_u.size_title as ad_unit_title,di.size_title as ad_di_title,color.title as color_title');
$this->db->from('default_new_buy_request as nbr');
$this->db->join('default_dmadata as dm', 'nbr.dma_id = dm.id', 'left');
$this->db->join('default_states as st', 'nbr.state_id = st.id', 'left');

      

        
        
        
      

    

nbr.dma_id

contains multiple comma (',') separated values ​​and compares to all dm.id

in default_dmadata

, but here it is just comparing only one value with dm.id

. In short, I need a function like explode () to compare each value against the second column.