alamb commented on code in PR #6904:
URL: https://github.com/apache/arrow-datafusion/pull/6904#discussion_r1259593868
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datafusion/physical-expr/src/aggregate/count.rs:
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@@ -76,6 +85,109 @@ impl Count {
}
}
+/// An accumulator to compute the counts of [`PrimitiveArray<T>`].
+/// Stores values as native types, and does overflow checking
+///
+/// Unlike most other accumulators, COUNT never produces NULLs. If no
+/// non-null values are seen in any group the output is 0. Thus, this
+/// accumulator has no additional null or seen filter tracking.
+#[derive(Debug)]
+struct CountGroupsAccumulator {
+ /// Count per group (use i64 to make Int64Array)
+ counts: Vec<i64>,
Review Comment:
I looked into this some more. The reason this count is `i64` is because the
output of `COUNT` is defined to be `DataType::Int64` and thus by using an i64
the output can be created directly. I will add a comment to clarify
```sql
❯ create table foo as values (1);
0 rows in set. Query took 0.004 seconds.
❯ select arrow_typeof(count(*)) from foo;
+-------------------------------+
| arrow_typeof(COUNT(UInt8(1))) |
+-------------------------------+
| Int64 |
+-------------------------------+
1 row in set. Query took 0.004 seconds.
```
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