Have you checked that you're reading from data and not cache, in each case?
http://en.helpdoc-online.com/powerbuilder_9.0/source/pbugp154.htm
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden