Query Custom laravel

$data = DB::select(DB::raw(
        "SELECT *
        FROM (
            SELECT
                calls.*,
                sys_rel.rel_to_module as module_name,
                sys_rel.rel_to_id as module_id,
                ( SELECT concat( leads.leads_first_name,' ', leads.leads_last_name)
                 FROM leads
                 WHERE leads.leads_serial_id =  module_id ) as rel_sys_name
            FROM calls
            JOIN sys_rel ON sys_rel.rel_serial_id = calls.rel_serial_id
            WHERE sys_rel.rel_to_module = 'leads' AND calls.rel_serial_id  > 0

                UNION ALL

            SELECT
                calls.*,
                sys_rel.rel_to_module as module_name,
                sys_rel.rel_to_id as module_id,
                ( SELECT concat( contacts.contacts_first_name,' ', contacts.contacts_last_name)
                 FROM contacts
                 WHERE contacts.contacts_serial_id =  module_id ) as rel_sys_name
            FROM calls
            JOIN sys_rel ON sys_rel.rel_serial_id = calls.rel_serial_id
            WHERE sys_rel.rel_to_module = 'contacts' AND calls.rel_serial_id  > 0

                UNION ALL

            SELECT
                calls.*,
                sys_rel.rel_to_module as module_name,
                sys_rel.rel_to_id as module_id,
                ( SELECT org_name
                 FROM org
                 WHERE org.org_serial_id =  module_id ) as rel_sys_name
            FROM calls
            JOIN sys_rel ON sys_rel.rel_serial_id = calls.rel_serial_id
            WHERE sys_rel.rel_to_module = 'org' AND calls.rel_serial_id  > 0

        ) as datatable
        order by rel_sys_name DESC"));