Unlike other adapters, the sqlserver adapter processes the order option and wipes it when using functions.
Here we can see a "ASC" inserted in the COALESCE call:
irb(main):001:0> Issue.order("coalesce(estimated_hours, 0), id").to_sql
=> "SELECT [issues].* FROM [issues] ORDER BY coalesce(estimated_hours ASC, 0) ASC, id ASC"
This does not happen when passing the order SQL fragments separately.
