find_by_sql with named parameterized sql

The latter isn't working because you are inserting symbols directly in
the sql, and as far as I know this isn't allowed. What's wrong with
using the first alternative?

By the way, I reccomend doing this instead:

@order = Order.find(:all, :conditions => ["amount > ? and quantity >
?", @amount, @quantity]

Just in case you feel like making the orders table a legacy table
called "15_t_orders" or whatever, you're keeping your app DRY by using
the rails finders instead of sql, and only having the data finding
itself in the sql part.