Can we optimize an ORDER BY clause?

Here's a small question for Oracle programmers.

I come from a Sybase back ground. I noticed that Oracle doesn't have the concept of a "clustered" index. In Sybase, a clustered index forces the physical order of records on disk to be the same as the logical order of the index. In a SELECT statement, if I use an ORDER BY clause on the columns that have the clustered index, then the server immediately start to return rows without actually performing the sort (because the sort would be unnecessary.)

In Oracle, is there a way I can optimize an ORDER BY clause so that the server will not build an intermediate result set for sorting?

Thanks for any advice.

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