MySQLi is a PHP extension. It's just a series of functions to access a MySQL server. Perl has nothing to do with it, you do not need to change your Perl scripts.

Hello,

As mentioned by @dimitri , MySQLi is just a library for PHP, it replaces the previous MySQL PHP library because it's "improved" (the "i"), so PHP depreciated the former MySQL PHP library.

That being said, if you are in a process of rewriting / reviewing your code , you should use the PHP PDO class [php.net...] , this is safer and more future proof . The PDO class provides a series of function to do any kind of DB manipulations, and it independent from the DB engine. So , for example, if one day, you decided to switch from MySQL to another DB engine, you'll be able to keep your code, and just change the db engine, when you create the PDO object.

technically speaking, DBI is perl's DB-independent interface and DBD::mysql is the mysql-specific interface.
therefore PHP's MySQL(i) is more equivalent to DBD::mysql than to DBI.