|Subject||RE: [firebird-support] index selectivity|
> http://www.firebirdfaq.org/faq167/Yes, unless you can combine the Boolean field with another filed which is used very commonly is your SELECTs.
> 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?
Otherwise, you should not index a low selectivity field (boolean) the cost* of the index is not worth it.
*Cost includes several factors,, including the extra I/O operations required to maintain the index as well as the fact that the engine might want to include the field/index into a SELECT which would result in a slower performing statement.