passenger.rb

SELECT p.id, par.first_name ||' '|| par.last_name  AS partners_name,
       c.first_name         ||' '|| c.last_name    AS customers_name,
       en_c.first_name      ||' '|| en_c.last_name AS enquiry_customers_name, 
       coalesce(par.first_name||par.last_name, c.first_name||c.last_name, en_c.first_name||en_c.last_name, 'test') AS result 
FROM passengers p 
  LEFT JOIN customers c    ON p.customer_id = c.id 
  LEFT JOIN partners  par  ON p.partner_id = par.id 
  JOIN      enquiries e    ON p.enquiry_id = e.id 
  JOIN      customers en_c ON e.customer_id = en_c.id 
ORDER BY coalesce(par.first_name||' '||par.last_name, c.first_name||' '||c.last_name, en_c.first_name||' '||en_c.last_name)
LIMIT 20000;