I do have "Programming the Perl DBI". It's a nice intro to the DBI (and to data stores without DBI), but not really helpful. When doing databases with Perl, it is much more important to understand the other end of the equation. I started learning on the Perl end, using that book, and was as lost afterwards as I was to begin with.

You need to grok relational databases first. Get a book on database design in general.

SQL will be introduced along the way and understanding it will come naturally, and at that point DBI will be trivial to figure out. Learning DBI is negligible compared to what it interfaces with, and starting with DBI would be a mistake.