mapleFU commented on code in PR #35989:
URL: https://github.com/apache/arrow/pull/35989#discussion_r1229897390
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cpp/src/parquet/statistics.cc:
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@@ -552,12 +560,19 @@ class TypedStatisticsImpl : public TypedStatistics<DType>
{
void Merge(const TypedStatistics<DType>& other) override {
this->num_values_ += other.num_values();
- if (other.HasNullCount()) {
+ // Merge always runs when Merge builder's page statistics
+ // into column chunk statistics, so it tent to have null count.
+ if (ARROW_PREDICT_TRUE(other.HasNullCount())) {
this->statistics_.null_count += other.null_count();
+ } else {
+ this->has_null_count_ = false;
}
- if (other.HasDistinctCount()) {
- this->statistics_.distinct_count += other.distinct_count();
+ // Distinct count cannot be merged.
Review Comment:
https://github.com/apache/arrow/commit/43c7154894f819e617dbf3d669dbe1185f05893b#diff-f8a090a40e214aba5ebff534411a9febf213b725597afb750395d2a7483d9bc1
I guess these code is written in 2016 and never changed the syntax for add
distinct count. Maybe it's designed like dictionary in Arrow IPC Streaming?
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