Re: Mystery query

[Phillip Ward]

Because MySQL is having to run three queries in series:
(1) select from order_details, based no Product Id, then
(2) select from orders, based on Order Id , then
(3) select from customers, based on Customer Id.
Even with proper indexing, there's no way MySQL can evaluate that query any other way.

This might be a little better, playing to MySQl's strengths:

   select c.CompanyName 
   ,      c.City 
   ,      c.Country
   from       customers c 
   inner join order o 
           on c.CustomerId = o.customerid 
   inner join order_details od 
           on o.OrderId = od.OrderId 
   where od.ProductId = 34 ;

Regards, Phill W.