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From Bram Biesbrouck <bram.biesbro...@reinvention.be>
Subject Re: Question regarding negated block join queries
Date Mon, 17 Jun 2019 18:32:27 GMT
On Mon, Jun 17, 2019 at 7:11 PM Shawn Heisey <apache@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.

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