IIRC, there are several issues regarding SQL, not only those regarding
joins. I seem to remember some issues with character conversion, RRN,
cursor management, among others.
Besides SQL, there are (among many others) some changes in C++ and Java
and, of course, Rob's favorite commands (CPYFRMIMPF/CPYTOIMPF) have some
differences regarding the error messages they return. As always, the "Memo
to Users" are a must read.
There are several and (sometimes important) changes when going from V5R4 to
V7R1. Nevertheless, I believe that the upgrade is worth doing, not only for
the (very valid) reasons Rob gave but because, as I see it, every new
release does implement new tools that allows us (developers) to create
better applications for our users.
My 0.02 cents :-)
IBM Certified Systems Expert — eServer i5 iSeries