http://www.firebirdfaq.org/faq167/

Hello, I've been reading this FAQ and I undestand that having an index on a
boolean field is the worst of the cases. But I've also seen that if you have (as
in my case) very little "active" records (MyBoolean = 1) and a LOT of inactive
records, is good to have an index to select the active records.

Is that True? Should I create an index on my boolean field?

Thanks!!!

-s