For those working with DB2 for i (AS/400, iSeries and later), IBM Data Studio can be worth obtaining and learning. It has numerous useful development features. But for debugging, you'll need to do a lot of learning to get it to work at all (if ever). Data Studio can be used for debugging if IBM i 6.1 or 7.1 is on the server and DB2 Group PTF level is at least up to mid-2013 levels. (V5R4 might also be possible, though there are contradictory statements at IBM sites; and I've seen no indication of needed PTFs.)
While trying to use Data Studio for debugging, you'll have results much sooner by downloading and installing iSeries Navigator from the server. Make sure that the minimum install includes the 'Database' component. (Not 'Data Transfer' which is essentially unrelated and requires licensing.) The 'Database' component gives access to 'Run SQL scripts' for AS/400 databases, and includes connections to the system graphical debugger.
Many other direct database functions are also included. The iNav feature downloads, installs and configures quite a bit faster than Data Studio. It's also easier to learn and fits better on smaller monitors. (Be aware that a recent iNav fix pack should also be applied.) But it is not a truly high-level database IDE. It simply provides the needed features for much of the database work other than major project development.
If you have no control over the fix levels on the server, or the server version isn't current, you might have no other good choice, especially for debugging of stored procs, etc.