gruuya commented on code in PR #9007:
URL: https://github.com/apache/arrow-datafusion/pull/9007#discussion_r1467552549
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datafusion/physical-plan/src/joins/utils.rs:
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@@ -955,7 +955,12 @@ fn max_distinct_count(
let result = match num_rows {
Precision::Absent => Precision::Absent,
Precision::Inexact(count) => {
- Precision::Inexact(count -
stats.null_count.get_value().unwrap_or(&0))
+ // To safeguard against inexact number of rows (e.g. 0)
being smaller than
+ // an exact null count we need to do a checked subtraction.
+ match
count.checked_sub(*stats.null_count.get_value().unwrap_or(&0)) {
+ None => Precision::Inexact(0),
Review Comment:
This made more sense than `Precision::Absent`.
Also, I'm not sure whether this can happen below as well, i.e. an inexact
null count being larger than an exact row count.
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