When a T-SQL query contains an
ORDER BY or
DISTINCT clause, a worktable is often required to process the final result of the query if it cannot determine that the rows will already be retrieved in the desired sort order or that a unique key in the result makes the rows distinct. If a query requires a worktable, that adds extra overhead and I/O to put the results into the worktable in
tempdb and do the sorting necessary to order the results or to eliminate duplicate rows. This can result in extended processing time for the query, which can delay the time it takes for the final result to be returned to the client application.
If it is not absolutely necessary for the rows returned to the application ...