Re: Index on boolean column

[Alec.Cawley]

Du?an Pavlica <pavlica@stripped> wrote on 30/03/2005 16:35:40:

> Hello,
> 
> maybe this is a silly question but how useful it is to create 
> indexes on columns containing only values 0 and 1 (true and false)?

Since I believe that MySQL ignores indexes if it expects to get more than 
30% hits, it will probably be ignored unless the distribution of 0s and 1s 
is very skewed. If you only have a tiny fraction of (say) 1s, it might be 
useful to extract that tiny fraction - but useless for the opposite.

        Alec