kaijianding opened a new pull request #11379:
URL: https://github.com/apache/druid/pull/11379
### Description
Sql like "select city_id, time_floor(__time to day), count(*) as c from
table group by city_id, time_floor(__time to day)", the original translated
query is granularity=all and dimensions:[d0, d1, c]
The better plan is granularity=day and dimensions:[d0] which reduces the
computation cost in historical/realtime node.
After this patch, a 5x performance improve is noticed from 5s to 900ms.
example sql:
```sql
select
sum("count") as c,
Floor(__time to DAY) as __time
from
"test_table"
__time >= TIMESTAMP '2021-05-19 00:00:00'
and __time < TIMESTAMP '2021-05-20 23:59:59'
group by
Floor(__time to DAY)
having
c > 0
```
```json
[
{
"c": 104236286,
"__time": "2021-05-19T00:00:00.000+08:00"
},
{
"c": 12162156,
"__time": "2021-05-20T00:00:00.000+08:00"
}
]
```
<hr>
##### Key changed/added classes in this PR
* `GroupByStrategyV2`
* `GroupByQuery`
* `DruidQuery`
<hr>
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- [x] been tested in a test Druid cluster.
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