Dandandan commented on code in PR #17606:
URL: https://github.com/apache/datafusion/pull/17606#discussion_r2354418549
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datafusion/functions-aggregate/src/count.rs:
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@@ -746,12 +746,25 @@ fn null_count_for_multiple_cols(values: &[ArrayRef]) ->
usize {
/// more efficient such as [`PrimitiveDistinctCountAccumulator`] and
/// [`BytesDistinctCountAccumulator`]
#[derive(Debug)]
-struct DistinctCountAccumulator {
+pub struct DistinctCountAccumulator {
values: HashSet<ScalarValue, RandomState>,
Review Comment:
We don't need to track whether the values are distinct, we already know when
all hashes are unique after building the map (number of hashes in the table
equals number of rows). There is a method `is_unique` (or similar) that does
the calculation.
I suggest we calculate the min/max after loading the values in memory
@jonathanc-n and only when all hashes have a single row mapping.
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