Not sure what is the problem but couple of hints/ideas:
- DBI returns undef if database cell contains NULL. May be there is a problem in your database.
- There is one problem with your query. You use astersk in it but in most cases it is bad idea. Check this node and this node for explanation why.
- One wierd thing. For me (perl 5.6.1) Data::Dumper prints undef when it encounters undefined value in data structure. In your output I see just ''. What does it mean? Well,.. I don't know :(