# What is the preferred way to run a filter-only query in 2.x?
**URL:** https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156
**Category:** Elasticsearch
**Created:** [September 21, 2016, 4:31pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156 "2016-09-21T16:31:48Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@jpblair](https://discuss.elastic.co/u/jpblair)
#### Post date: [September 21, 2016, 4:31pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/1 "2016-09-21T16:31:48Z")
I'm currently migrating from 1 to 2 and trying to wrap my head around the merging of filters and queries. Based on the documentation [here](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-filtered-query.html), I see that in 2.x, when trying to execute a query that includes both a query and a filter, these should be wrapped into a `bool` query with the query as the `must` clause and the filter as the `filter` clause. So if I _only_ have a filter (assuming it is a `bool` filter, as those existed in 1.x), with no query, what is the preferred way to do that?
- Wrap the filter into another `bool` filter as the `must` clause.
- Wrap the filter into another `bool` filter as the `filter` clause (with no `must` clause).
- Pass the filter as the top-level `query` since the "filter" is actually a `bool` query now.
How are these options different (or are they the same), with respect to results returned, performance, idiomatic-ness, etc.?
I am currently using the third approach, mostly because it was the path of least resistance. However, since my filter construction logic was written based on Elasticsearch 1.x, all of the subclauses are under `must`, rather than `filter`. Does that mean by executing this filter as a top-level `query`, the subfilters are actually being executed in query context? Do I need to go and change every single `must` in all of my nested `bool` filters to `filter`? Apologies if this question has already been answered elsewhere. Thanks.
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### Author:  [@mikemccand](https://discuss.elastic.co/u/mikemccand)
#### Post date: [September 21, 2016, 6:55pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/2 "2016-09-21T18:55:35Z")
The best way to think of `filter` is that it's really a `must` query with score of 0. There really is no such thing as a "filter" anymore. BQ only separates `must` and `filter` because `filter` means "do not alter the scores".
Lucene generally will rewrite a single-clause BQ nested into another BQ, so I suspect all three of your options are executed the same: same performance, same scores.
I would suggest you just do the 3rd option since it's the most straightforward.
It is worth changing `must` to `filter` in your app, if scoring is not important, because Lucene optimizes this, e.g. by not bothering to load/decode per-doc term frequency information when scoring.
Mike McCandless
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### Author:  [@jpblair](https://discuss.elastic.co/u/jpblair)
#### Post date: [September 21, 2016, 7:12pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/3 "2016-09-21T19:12:29Z")
> I suspect all three of your options are executed the same: same performance, same scores. I would suggest you just do the 3rd option since it's the most straightforward.
--
> It is worth changing must to filter in your app, if scoring is not important, because Lucene optimizes this, e.g. by not bothering to load/decode per-doc term frequency information when scoring.
I'm a little confused - don't these two statements contradict each other? And on the second point, do you mean changing from `must` to `filter` in each of the nested filters (sorry, BQs - it'll take me a while to get used to that 🙂 ), or just top-level?
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### Author:  [@mikemccand](https://discuss.elastic.co/u/mikemccand)
#### Post date: [September 21, 2016, 10:55pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/4 "2016-09-21T22:55:19Z")
> [@jpblair](#):
>
> I'm a little confused - don't these two statements contradict each other?
Oh, sorry, I mis-understood your option 3. If you have only a single `filter` you want to run, you should just put that into a single `bool` query, e.g.:
```auto
{
"bool" : {
"filter": {
...
}
}
}
```
This is more efficient than just using your query directly (your option 3) since Lucene will avoid computing scores. I think this was your option 2.
> [@jpblair](#):
>
> And on the second point, do you mean changing from must to filter in each of the nested filters (sorry, BQs - it'll take me a while to get used to that 🙂 ), or just top-level?
Sorry for the BQ acronym!
It should be sufficient to only change to `filter` in the top-level `bool` query: Lucene will take care of ignoring (and not computing) scores of the nested clauses under that even if you use `must` inside those.
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### Author:  [@jpblair](https://discuss.elastic.co/u/jpblair)
#### Post date: [September 26, 2016, 8:44pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/5 "2016-09-26T20:44:51Z")
Thanks for your help. I'll have to give that a try.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 5, 2017, 10:17pm UTC](https://discuss.elastic.co/t/what-is-the-preferred-way-to-run-a-filter-only-query-in-2-x/61156/6 "2017-07-05T22:17:11Z")