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docs: Clarify first_value usage in select vs aggregate #1348

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Merged
timsaucer merged 3 commits into from
Feb 12, 2026
Merged

docs: Clarify first_value usage in select vs aggregate #1348

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38322b3
docs: Add warning to first_value about usage in select vs aggregate
AdMub Jan 22, 2026
d7b3ab5
chore: remove temporary reproduction script
AdMub Jan 22, 2026
c7b3663
Update all aggregate functions to have an example usage that is correct
timsaucer Feb 11, 2026
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5 changes: 5 additions & 0 deletions python/datafusion/functions.py
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Expand Up @@ -2268,6 +2268,11 @@ def first_value(
) -> Expr:
"""Returns the first value in a group of values.

.. note::
This is an aggregate function. It must be used within
:py:meth:`~datafusion.dataframe.DataFrame.aggregate` and generally cannot be
used with :py:meth:`~datafusion.dataframe.DataFrame.select`.

This aggregate function will return the first value in the partition.

If using the builder functions described in ref:`_aggregation` this function ignores
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