Some queries that include distinct use a sort step to enforce the uniqueness of values in the result set. distinct queries and order by queries do not require the sorting step when the index used to locate rows supports the order by or distinct clause.
For those cases where the sort is performed, the distinct keyword in a select list and the order by clause share some showplan messages:
Each generates a worktable message.
The message “This step involves sorting.”.
The message “Using GETSORTED”.