RE: MySQL AB: Need documentation clarification

[Jon Frisby]

> Indexes are only used if they significantly reduce the number of reads
> required vs a full table scan (I believe 30% is mysql's threshhold).
> An IS NOT NULL clause may very well use an index if almost all of the
> records have NULL in that particular field.  A != clause is a bit
> harder, since that basically devolves into "field < ## OR field > ##",
> and I don't think can optimize that.

In my circumstance, over 90% of the rows have a NULL in the relevant column,
so IS NOT NULL should definitely be using the index.

-JF