Ted-Jiang opened a new pull request #1841:
URL: https://github.com/apache/arrow-datafusion/pull/1841
# Which issue does this PR close?
Closes #1823.
# Rationale for this change
test result:
```
1million_1million.parquet
+----------------------------+
| COUNT(DISTINCT test.value) |
+----------------------------+
| 631504 |
+----------------------------+
1 row in set. Query took 1.225 seconds.
+---------------------------------+
| BITMAPCOUNTDISTINCT(test.value) |
+---------------------------------+
| 631504 |
+---------------------------------+·
1 row in set. Query took 0.175 seconds(roaring-rs).
+---------------------------------+
| BITMAPCOUNTDISTINCT(test.value) |
+---------------------------------+
| 631504 |
+---------------------------------+
1 row in set. Query took 0.052 seconds （croaring-rs）.
+----------------------------+
| APPROXDISTINCT(test.value) |
+----------------------------+
| 630261 |
+----------------------------+
1 row in set. Query took 0.052 seconds.
```
So, choose [croaring-rs](https://github.com/saulius/croaring-rs) bitmap for
more efficient.
## What changes are included in this PR?
Add new `aggregate_function` called bitmap_distinct
## Are there any user-facing changes?
Maybe we can add one optimize rule to like `approx_median()`, change
`count(distinct x)` to `bitmap_distinct` in future
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