Over at Ask The Oracle Expert: Questions & Answers comes this.
I obviously don't have the patience to be an Oracle expert because I would have been tempted to tell the person that elicited that response to RTFM.
Notice how TableB occurs twice in the query. This means we must use an alias for each occurrence, and also use the appropriate alias to qualify the columns in the SELECT clause. And since the columns from the two instances of TableB have the same name, it is also common—but not required—to assign column aliases in the SELECT clause.
I obviously don't have the patience to be an Oracle expert because I would have been tempted to tell the person that elicited that response to RTFM.