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Add test to verify count aggregate function should not be nullable #12085

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Add test to verify count aggregate function should not be nullable #12085

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9d3a47f
Fix: count aggregate function should not be nullable
Aug 20, 2024
28a5b9b
Merge branch 'apache:main' into datafusion
HuSen8891 Aug 21, 2024
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12 changes: 11 additions & 1 deletion datafusion/physical-plan/src/aggregates/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@ use datafusion_physical_expr::{
LexRequirement, PhysicalExpr, PhysicalSortRequirement,
};

use datafusion_physical_expr_functions_aggregate::aggregate::AggregateFunctionExpr;
use itertools::Itertools;

pub mod group_values;
Expand Down Expand Up @@ -817,7 +818,16 @@ fn create_schema(
| AggregateMode::SinglePartitioned => {
// in final mode, the field with the final result of the accumulator
for expr in aggr_expr {
fields.push(expr.field()?)
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let aggregte_func_expr =
expr.as_any().downcast_ref::<AggregateFunctionExpr>();
// count should not be nullable
if aggregte_func_expr.is_some()
&& aggregte_func_expr.unwrap().fun().name() == "count"
{
fields.push(expr.field()?.with_nullable(false))
} else {
fields.push(expr.field()?)
}
}
}
}
Expand Down
5 changes: 5 additions & 0 deletions datafusion/sqllogictest/test_files/aggregate.slt
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Expand Up @@ -5364,6 +5364,11 @@ SELECT MAX(col0) FROM empty WHERE col0=1;
----
NULL

query I
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@alamb alamb Aug 20, 2024

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On main this query fails like this:

creatDataFusion CLI v41.0.0
> create table empty;
0 row(s) fetched.
Elapsed 0.008 seconds.

> select distinct count() from empty;
CombinePartialFinalAggregate
caused by
Internal error: PhysicalOptimizer rule 'CombinePartialFinalAggregate' failed, due to generate a different schema, original schema: Schema { fields: [Field { name: "count()", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} }, new schema: Schema { fields: [Field { name: "count()", data_type: Int64, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} }.
This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker

select distinct count() from empty;
----
0

query TT
EXPLAIN SELECT MIN(col0) FROM empty;
----
Expand Down