bkietz commented on code in PR #43726:
URL: https://github.com/apache/arrow/pull/43726#discussion_r1744532207
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cpp/src/arrow/dataset/file_parquet.cc:
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@@ -366,9 +366,16 @@ std::optional<compute::Expression>
ParquetFileFragment::EvaluateStatisticsAsExpr
const parquet::Statistics& statistics) {
auto field_expr = compute::field_ref(field_ref);
+ bool may_has_null = !statistics.HasNullCount() || statistics.null_count() >
0;
+ bool must_has_null = statistics.HasNullCount() && statistics.null_count() >
0;
// Optimize for corner case where all values are nulls
- if (statistics.num_values() == 0 && statistics.null_count() > 0) {
- return is_null(std::move(field_expr));
+ if (statistics.num_values() == 0) {
+ if (must_has_null) {
+ return is_null(std::move(field_expr));
+ }
+ // If there are no values and no nulls, it might be empty or contains
+ // only null.
+ return std::nullopt;
Review Comment:
I think it's simpler and more consistent to return
`is_null(std::move(field_expr))` if we can; in general I think it usually makes
the most sense to construct the most explicit/precise guarantees which are
easily available (and therefore to avoid making this special case which will
result in *less* specific guarantees).
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