Silvio Matthes <silvio.matthes@xcom.de> writes:
> 2.) Would it be wiser to change all the empty values to some placeholder
> (e.g. 'empty')?
You're missing the point entirely. '' is being treated specially
because the planner can see from the column statistics that it occurs a
lot. Substituting a different value would simply move the problem over
to that value (as soon as you'd done ANALYZE, anyway).
regards, tom lane