# Query optimisation: must vs must\_not order
**URL:** https://discuss.elastic.co/t/query-optimisation-must-vs-must-not-order/107248
**Category:** Elasticsearch
**Created:** [November 10, 2017, 9:27pm UTC](https://discuss.elastic.co/t/query-optimisation-must-vs-must-not-order/107248 "2017-11-10T21:27:53Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@a06ced31bae02498a46d](https://discuss.elastic.co/u/a06ced31bae02498a46d)
#### Post date: [November 10, 2017, 9:27pm UTC](https://discuss.elastic.co/t/query-optimisation-must-vs-must-not-order/107248/1 "2017-11-10T21:27:54Z")
Hello,
I use ElasticSearch 2.3.
I observed that with this simple query order of `must` and `must_not` conditions in query JSON matter:
```
{
"query": {
"bool": {
"filter": {
"bool": {
"must": { "term": { "group_id": 1 } },
"must_not": {
"regexp": { "category": { "value": ".*value.*", "flags": "NONE" } }
}
}
}
}
}
}
```
When `must` goes first, query is more than 10 times faster than if `must_not` key goes first in bool object. I think it makes sense given that `must` condition reduces amount of documents in question significantly and then filtering them by `regexp` is much faster as opposed to first filter by `regexp` and then by `group_id`.
Now when I try to run same query for another group\_id (e.g. `group_id: 2`) this optimisation doesn't work. Regardless of `must` and `must_not` order it takes roughly the same amount of time – approximately equal to the time taken by the first unoptimised query for the first group.
Number of documents in both groups is of the same magnitude and the resulting output is similar in a way that most of records from the group are returned and only small percentage of them are filtered out because of the `must_not` condition.
My goal now is to compare query execution profiles for both groups and figure out what makes `group_id = 1` so special that optimisation is so helpful. And eventually figure out how to make optimisation work for the second group (and all other groups).
I ran this query for both groups with `profile: true` but couldn't find no information that would help me figure this out.
I checked Lucene query string produced for the second group and regardless of whether `regexp` condition is before `group_id` condition or not query takes roughly the same time.
Do you have any ideas how I can figure out what makes the difference between those groups and eventually make this query faster for the second group?
Thank you in advance!
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [December 8, 2017, 9:27pm UTC](https://discuss.elastic.co/t/query-optimisation-must-vs-must-not-order/107248/2 "2017-12-08T21:27:58Z")
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