the profiling tool works fine but I have to modify the profile_mysqli.php to use it on a windows system (WAMPP).

Good to hear. The script was quick and dirty so it's not suprising that you had to change it for Windows.

I test it and it seems(!) that the INNER JOIN is a little bit faster that the query that uses an IN() condition. Can someone confirm this behaviour?

I'm not a database expert so I don't know.

Regards,
Daniel