I see DBD/mysql.pm includes "use DBI;", so it wasn't needed explicitly in your code in that case. However, even the DBD::mysql examples start out with "use DBI;", and the connect method induces loading the corresponding DBD module (instead of useing it explicitly). This way - at least for simple SQL - you could switch and mix database drivers by simply changing the connect string...

⇒ You might need to install DBI and/or DBD::mysql, because at least one of these two seems not to be in XAMPP's default - (see also)