On Mon, Jun 17, 2019 at 7:11 PM Shawn Heisey <apa...@elyograg.org> wrote:
> On 6/17/2019 4:46 AM, Bram Biesbrouck wrote:
> > q={!parent which=-(parentUri:*)}*:*
>
> Pure negative queries do not work in Lucene. Sometimes, when you do a
> single-clause negative query, Solr is able to detect the problem and
> automatically make an adjustment so the query works. This happens
> transparently so you never notice.
>
> In essence, what your negative query tells Lucene is "start with
> nothing, and then subtract docs that match this query." Since you
> started with nothing and then subtracted, you get nothing.
>
> Also, that's a wilcard query. Which could be very slow if the possible
> number of values in parentUri is more than a few. If that field can
> only contain a very small number of values, then a wildcard query might
> be fast.
>
> The following query solves both problems -- starting with all docs and
> then subtracting things that match the query clause after that:
>
> *:* -parentUri:[* TO *]
>
> This will return all documents that do not have the parentUri field
> defined. The [* TO *] syntax is an all-inclusive range query.
>
Hi Shawn,
Awesome elaborate explanation, thank you. Also thanks for the optimization
hint. I found both approaches online, but didn't realize there was a
performance difference .
Digging deeper, I've found this SO post, basically explaining why it worked
some of the time, but not in all cases:
https://stackoverflow.com/questions/10651548/negation-in-solr-query
best,
b.
