Both order by clauses and commands that create indexes can use the asc or desc (ascending or descending) ordering qualifications:
For index creation, the asc and desc qualifications specify the order in which keys are to be stored in the index.
In the order by clause, the ordering qualifications specify the order in which the columns are to be returned in the output.
To avoid a sort when using a specific index, the asc or desc qualifications in the order by clause must either be exactly the same as those used to create the index, or must be exactly the opposite.
