# \[Theoretical\] How does query filtering upon nested aggregation work?

**URL:** <https://discuss.elastic.co/t/theoretical-how-does-query-filtering-upon-nested-aggregation-work/204072>\
**Category:** Elasticsearch\
**Created:** [October 17, 2019, 2:06pm UTC](https://discuss.elastic.co/t/theoretical-how-does-query-filtering-upon-nested-aggregation-work/204072 "2019-10-17T14:06:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![randomuser](https://avatars.discourse-cdn.com/v4/letter/r/958977/32.png) [@randomuser](https://discuss.elastic.co/u/randomuser)\
**Post date:** [October 17, 2019, 2:06pm UTC](https://discuss.elastic.co/t/theoretical-how-does-query-filtering-upon-nested-aggregation-work/204072/1 "2019-10-17T14:06:07Z")

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I've just used a really neat option - filtering upon nested aggregation values. I love it, it works the way it's supposed to, but I'm interested in how does it work and in which order are the filters/aggregations executed.

This would be a sample query to get the point across:

```
"query": {
  "bool": {
    "must"" [ 
      {
         "term": {
           "car_producer": "Mercedes" 
         }
      },
      {
         "terms": {
           "nested_aggregation": [4, 8]
         }
      }
    ]
  }
},
"aggs": {
  "agg_results": {
      "terms": {
          "field": "carModels"
       },
       "aggs": {
          "nested_aggregation": {
             "terms": {
                "field": "colours"
             }
          }
       }
   }
}

```

As you can see, we are filtering all the **Mercedes** cars.  
In the first aggregation, we're aggregating all the **car model** which Mercedes produced.  
In the nested aggregation, we're aggregating the number of **colours** for each **car model**.  
If we go back to the second term clause in the query part, we want to display results only for cars which have exactly **4 or 8 cars** of one **colour** for a specific **car model**.

This example is completely made up, but I hope that it gets the point across.

- How does this actually work?

- In what order are the queries and aggregations executed?

- Does this part of the query:

- From what I've noticed, in the "hits" it will return **all** the results even for aggregated buckets whose doc count is larger than 1 (in case 4 aggregated buckets, all will be shown in the hits)?

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [November 14, 2019, 2:06pm UTC](https://discuss.elastic.co/t/theoretical-how-does-query-filtering-upon-nested-aggregation-work/204072/2 "2019-11-14T14:06:18Z")

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