# Nested Query vs. Has Child Query **URL:** \ **Category:** Elasticsearch\ **Created:** [January 10, 2013, 11:34pm UTC](https://discuss.elastic.co/t/nested-query-vs-has-child-query/10304 "2013-01-10T23:34:41Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![otisg](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/otisg/32/492_2.png) [@otisg](https://discuss.elastic.co/u/otisg)\ **Post date:** [January 10, 2013, 11:34pm UTC](https://discuss.elastic.co/t/nested-query-vs-has-child-query/10304/1 "2013-01-10T23:34:41Z")
Hi, What exactly is the difference between a Nested Query and a Has Child Query? Is the main difference around the indexing and updating (all docs in case of nested docs and individual docs in case or parent-child docs)? When is the former better or more appropriate than the latter? Is there inherent (search) performance difference? ## Thanks, Otis ELASTICSEARCH Performance Monitoring - [http://sematext.com/spm/index.html](http://sematext.com/spm/index.html) -- ---
**Author:** ![Lukas\_Vlcek1](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/lukas_vlcek1/32/819_2.png) [@Lukas\_Vlcek1](https://discuss.elastic.co/u/Lukas_Vlcek1)\ **Post date:** [January 11, 2013, 11:32am UTC](https://discuss.elastic.co/t/nested-query-vs-has-child-query/10304/2 "2013-01-11T11:32:36Z")
Hi Otis, the last time I was looking at this the advantage of Nested Documents is better performance but less flexibility as opposed to Parent/Child documents. The performance of Nested Documents is driven by Lucene level implementation. Check [http://lucene.apache.org/core/3\_6\_1/api/all/org/apache/lucene/search/join/ToParentBlockJoinQuery.htmlfor](http://lucene.apache.org/core/3_6_1/api/all/org/apache/lucene/search/join/ToParentBlockJoinQuery.htmlfor) more details. The downside is that any update in parent or child documents means reindexing of whole block. Lukas On Fri, Jan 11, 2013 at 12:34 AM, Otis Gospodnetic \< [otis.gospodnetic@gmail.com](mailto:otis.gospodnetic@gmail.com)\> wrote: > Hi, > > What exactly is the difference between a Nested Query and a Has Child > Query? Is the main difference around the indexing and updating (all docs > in case of nested docs and individual docs in case or parent-child docs)? > > When is the former better or more appropriate than the latter? > > Is there inherent (search) performance difference? > > ## Thanks, Otis > > ELASTICSEARCH Performance Monitoring - [Sematext Monitoring | Infrastructure Monitoring Service](http://sematext.com/spm/index.html) > > -- -- ---
**Author:** ![otisg](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/otisg/32/492_2.png) [@otisg](https://discuss.elastic.co/u/otisg)\ **Post date:** [January 11, 2013, 6:50pm UTC](https://discuss.elastic.co/t/nested-query-vs-has-child-query/10304/3 "2013-01-11T18:50:43Z")
Hi Lukáš, ("I put diacritics back in your name" ;)) Ah, I see, ES uses Lucene's BlockJoinQuery for Nested Query, of course! Thanks for the pointer. Good explanation of what happens under the hood: > **[Searching relational content with Lucene's BlockJoinQuery](https://blog.mikemccandless.com/2012/01/searching-relational-content-with.html)** > > Lucene's 3.4.0 release adds a new feature called index-time join (also sometimes called sub-documents, nested documents or parent/child d... ## Otis ELASTICSEARCH Performance Monitoring - [Sematext Monitoring | Infrastructure Monitoring Service](http://sematext.com/spm/index.html) On Friday, January 11, 2013 6:32:36 AM UTC-5, Lukáš Vlček wrote: > Hi Otis, > > the last time I was looking at this the advantage of Nested Documents is > better performance but less flexibility as opposed to Parent/Child > documents. > > The performance of Nested Documents is driven by Lucene level > implementation. Check > [http://lucene.apache.org/core/3\_6\_1/api/all/org/apache/lucene/search/join/ToParentBlockJoinQuery.htmlfor](http://lucene.apache.org/core/3_6_1/api/all/org/apache/lucene/search/join/ToParentBlockJoinQuery.htmlfor) more details. > > The downside is that any update in parent or child documents means > reindexing of whole block. > > Lukas > > On Fri, Jan 11, 2013 at 12:34 AM, Otis Gospodnetic \<[otis.gos...@gmail.com](mailto:otis.gos...@gmail.com)\ > > > wrote: > > > Hi, > > > > What exactly is the difference between a Nested Query and a Has Child > > Query? Is the main difference around the indexing and updating (all docs > > in case of nested docs and individual docs in case or parent-child docs)? > > > > When is the former better or more appropriate than the latter? > > > > Is there inherent (search) performance difference? > > > > ## Thanks, Otis > > > > ELASTICSEARCH Performance Monitoring - [Sematext Monitoring | Infrastructure Monitoring Service](http://sematext.com/spm/index.html) > > > > -- -- ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 2:56am UTC](https://discuss.elastic.co/t/nested-query-vs-has-child-query/10304/4 "2017-07-06T02:56:51Z")