morrySnow opened a new pull request, #67881:
URL: https://github.com/apache/doris/pull/67881
## Problem
When an aggregate groups by a unique, non-null key, each group contains one
row. The planner used that fact to mark every `COUNT` and `NDV` output as
uniform. That is not true for nullable arguments: `COUNT(v)` and `NDV(v)`
return `0` for a null value and `1` for a non-null value. An outer aggregation
can consequently remove such an output from its group keys and merge rows that
must remain separate.
## Root cause
The logical and physical aggregate trait derivations classified an output as
uniform solely from the aggregate function class. They did not distinguish
`COUNT(*)` from argument-based aggregates or check whether the complete
argument expressions always participate in the aggregate.
## Reproduction
Create a unique-key table containing two rows whose nullable value differs:
```sql
create table uniform_agg_witness (
pk int not null,
b int not null,
v int null
) unique key(pk)
distributed by hash(pk) buckets 1
properties("replication_num"="1");
insert into uniform_agg_witness values (1, 7, null), (2, 7, 9);
select b, c, count(*) as n, sum(h) as sh
from (
select pk, b, count(v) as c, ndv(v) as h
from uniform_agg_witness
group by pk, b
) s
group by b, c
order by b, c;
```
The invalid uniform trait removed `c` from the outer group keys and produced
one merged row. The correct result has separate `(7, 0)` and `(7, 1)` groups.
## Fix
- Share one uniform-aggregate proof between logical and physical aggregate
plans.
- Keep `COUNT(*)` uniform for a single-row group.
- Treat argument-based `COUNT` and `NDV` as uniform only when every complete
argument expression is definitely non-null.
- Default all other cases to non-uniform. This conservatively rejects
nullable arguments, nullable conditional expressions, narrowing and try casts
whose result may be null, multi-argument counts with any nullable argument, and
null-extended outer-join outputs.
- Preserve the safe optimization for non-null arguments.
## Tests
- `./run-fe-ut.sh --run org.apache.doris.nereids.properties.UniformTest` (12
tests passed)
- `./build.sh --fe`
- `./run-regression-test.sh --run -f
regression-test/suites/nereids_rules_p0/eliminate_gby_key/eliminate_group_by_key_by_uniform.groovy
... -forceGenOut`
- Re-ran the same regression suite normally against the generated expected
output.
The regression asserts both results and plan group keys: nullable
`COUNT`/`NDV` remain in the outer grouping, while non-null `COUNT` still
permits safe group-key elimination.
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