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Posted to github@arrow.apache.org by "alamb (via GitHub)" <gi...@apache.org> on 2023/03/14 13:26:11 UTC
[GitHub] [arrow-datafusion] alamb opened a new issue, #5595: Make median return `null` on empty input rather than error
alamb opened a new issue, #5595:
URL: https://github.com/apache/arrow-datafusion/issues/5595
**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
@Jefffrey notes in https://github.com/apache/arrow-datafusion/pull/5560#pullrequestreview-1336092803 that we are inconsistent with polars, which seems to return null for empty inputs:
>>> df = pl.DataFrame({"foo": []})
>>> df.median()
shape: (1, 1)
┌──────┐
│ foo │
│ --- │
│ f32 │
╞══════╡
│ null │
└──────┘
>>>
**Describe the solution you'd like**
Be consistent with polars (return null) .
While postgres does not support `median` so we can't use its behavior as a guide, returning `null` on empty input would be consistent with the other sql aggregate functions such as `sum`
For example:
```sql
postgres=# create table t as values (1);
SELECT 1
postgres=# select median(column1) from t where column1 < 0;
ERROR: function median(integer) does not exist
LINE 1: select median(column1) from t where column1 < 0;
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
postgres=# select sum(column1) from t where column1 < 0;
sum
-----
(1 row)
```
**Describe alternatives you've considered**
Leave as error
**Additional context**
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[GitHub] [arrow-datafusion] alamb closed issue #5595: Make median return `null` on empty input rather than error
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #5595: Make median return `null` on empty input rather than error
URL: https://github.com/apache/arrow-datafusion/issues/5595
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[GitHub] [arrow-datafusion] toppyy commented on issue #5595: Make median return `null` on empty input rather than error
Posted by "toppyy (via GitHub)" <gi...@apache.org>.
toppyy commented on issue #5595:
URL: https://github.com/apache/arrow-datafusion/issues/5595#issuecomment-1470651513
Hi! I've never contributed before, but could take a look if this is up for grabs?
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[GitHub] [arrow-datafusion] alamb commented on issue #5595: Make median return `null` on empty input rather than error
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #5595:
URL: https://github.com/apache/arrow-datafusion/issues/5595#issuecomment-1470281984
I think this is a good first issue as the desired behavior is well defined and there are existing tests
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[GitHub] [arrow-datafusion] jhorstmann commented on issue #5595: Make median return `null` on empty input rather than error
Posted by "jhorstmann (via GitHub)" <gi...@apache.org>.
jhorstmann commented on issue #5595:
URL: https://github.com/apache/arrow-datafusion/issues/5595#issuecomment-1470266735
The corresponding postgres syntax would be
```
SELECT PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY column1) FROM ...
```
Which returns NULL on empty inputs.
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[GitHub] [arrow-datafusion] alamb commented on issue #5595: Make median return `null` on empty input rather than error
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #5595:
URL: https://github.com/apache/arrow-datafusion/issues/5595#issuecomment-1470656775
> Hi! I've never contributed before, but could take a look if this is up for grabs?
Please do @toppyy, and welcome!
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