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fix: set distinct_count to Absent when merging statistics #17385

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Merged
merged 1 commit into from
Sep 4, 2025
+47 −0
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fix: set distinct_count to Absent when merging statistics #17385

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47 changes: 47 additions & 0 deletions datafusion/common/src/stats.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -538,6 +538,7 @@ impl Statistics {
col_stats.max_value = col_stats.max_value.max(&item_col_stats.max_value);
col_stats.min_value = col_stats.min_value.min(&item_col_stats.min_value);
col_stats.sum_value = col_stats.sum_value.add(&item_col_stats.sum_value);
col_stats.distinct_count = Precision::Absent;
}

Ok(Statistics {
Expand Down Expand Up @@ -1152,4 +1153,50 @@ mod tests {
let e = Statistics::try_merge_iter(&items, &schema).unwrap_err();
assert_contains!(e.to_string(), "Error during planning: Cannot merge statistics with different number of columns: 0 vs 1");
}

#[test]
fn test_try_merge_distinct_count_absent() {
// Create statistics with known distinct counts
let stats1 = Statistics::default()
.with_num_rows(Precision::Exact(10))
.with_total_byte_size(Precision::Exact(100))
.add_column_statistics(
ColumnStatistics::new_unknown()
.with_null_count(Precision::Exact(0))
.with_min_value(Precision::Exact(ScalarValue::Int32(Some(1))))
.with_max_value(Precision::Exact(ScalarValue::Int32(Some(10))))
.with_distinct_count(Precision::Exact(5)),
);

let stats2 = Statistics::default()
.with_num_rows(Precision::Exact(15))
.with_total_byte_size(Precision::Exact(150))
.add_column_statistics(
ColumnStatistics::new_unknown()
.with_null_count(Precision::Exact(0))
.with_min_value(Precision::Exact(ScalarValue::Int32(Some(5))))
.with_max_value(Precision::Exact(ScalarValue::Int32(Some(20))))
.with_distinct_count(Precision::Exact(7)),
);

// Merge statistics
let merged_stats = stats1.try_merge(&stats2).unwrap();

// Verify the results
assert_eq!(merged_stats.num_rows, Precision::Exact(25));
assert_eq!(merged_stats.total_byte_size, Precision::Exact(250));

let col_stats = &merged_stats.column_statistics[0];
assert_eq!(col_stats.null_count, Precision::Exact(0));
assert_eq!(
col_stats.min_value,
Precision::Exact(ScalarValue::Int32(Some(1)))
);
assert_eq!(
col_stats.max_value,
Precision::Exact(ScalarValue::Int32(Some(20)))
);
// Distinct count should be Absent after merge
assert_eq!(col_stats.distinct_count, Precision::Absent);
}
}