This is a brief note with an odd history – and the history is more significant than the note.
While searching my library for an example of an odd costing effect for the “order by” clause I discovered a script that looked as if I’d written for 11.1.0.6 in 2008 to demonstrate a redundant sort operation appearing in an execution plan; and then I discovered a second script written for 11.2.0.4 in 2014 demonstrating a variant of the same thing (presumably because I’d not found the original script in 2014) and the second script referenced a MOS bug number
Bug 18701129 : SORT ORDER BY ISN’T AVOIDED WHEN ROWID IS ADDED TO ORDER BY CLAUSE
