On 8/9/07, Pieter Berkel <[EMAIL PROTECTED]> wrote: > From an theoretical IR standpoint, there is no reason to index null values, > or even empty strings for that matter. However in practice there are plenty > of cases that I've encountered where it is necessary to obtain a list of > documents where a particular field is null (i.e. hasn't been specified at > index time) or an empty string. > > For example, you may need to generate a list of products contained in your > index that do not have a part number. A dirty, ugly hack work-around to > this problem that we've used in the past is to replace null or unset values > at index time with a special token value like "__null__" that (hopefully) > won't appear in normal indexed data.
A null field (meaning no value) can be indexed by leaving it out, and searched with a negative filter or query clause: -field:[* TO *] -Yonik
