LakshSingla opened a new pull request #12065:
URL: https://github.com/apache/druid/pull/12065
### Description
Related to #11188
The above mentioned PR allowed timeseries queries to return a default
result, when queries of type: `select count(*) from table where
dim1="_not_present_dim_"` were executed. Before the PR, it returned no row,
after the PR, it would return a row with value of `count(*)` as 0 (as expected
by SQL standards of different dbs).
In `Grouping#applyProject`, we can sometimes perform optimization of a
groupBy query to a timeseries query if possible (when the keys of the groupBy
are constants, as generated by automated tools). For example, in `select
count(*) from table where dim1="_present_dim_" group by "dummy_key"`, the
groupBy clause can be removed. However, in the case when the filter doesn't
return anything, i.e. `select count(*) from table where
dim1="_not_present_dim_" group by "dummy_key"`, the behavior of general
databases would be to return nothing, while druid (due to above change) returns
an empty row. This PR aims to fix this divergence of behavior.
Example cases:
1. `select count(*) from table where dim1="_not_present_dim_" group by
"dummy_key"`.
_CURRENT_: Returns a row with count(*) = 0
_EXPECTED_: Return no row
2. `select 'A', dim1 from foo where m1 = 123123 and dim1 =
'_not_present_again_' group by dim1`
_CURRENT_: Returns a row with ('A', 'wat')
_EXPECTED_: Return no row
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To do this, a boolean `droppedDimensionsWhileApplyingProject` has been added
to `Grouping` which is true whenever we make changes to the original shape with
optimization. Hence if a timeseries query has a grouping with this set to true,
we set `skipEmptyBuckets=true` in the query context (i.e. donot return any row).
<hr>
##### Key changed/added classes in this PR
* `Grouping.java`
* `DruidQuery#toTimeseriesQuery`
<hr>
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- [ ] using the [concurrency
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- [ ] added documentation for new or modified features or behaviors.
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- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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