Improving docs

Author: renato2099

docs/source/user-guide/common-operations/joins.rst

@@ -78,6 +78,10 @@ Full Join
 A full join merges rows from two tables based on a related column, returning all rows from both tables, even if there
 is no match. Unmatched rows will have null values.
 
+The drop_duplicate_keys option is not supported for FULL JOINs because left and right join key columns may contain
+non-equivalent values (including NULLs). For FULL JOINs, both key columns are always preserved and users should perform
+explicit post-processing if desired.
+
 .. ipython:: python
 
     left.join(right, left_on="customer_id", right_on="id", how="full")

python/datafusion/dataframe.py

@@ -832,6 +832,10 @@ def join(
             drop_duplicate_keys: When True, the columns from the right DataFrame
                 that have identical names in the ``on`` fields to the left DataFrame
                 will be dropped.
+                This option is not supported for FULL JOINs because left and right join
+                key columns may contain non-equivalent values (including NULLs). For
+                FULL JOINs, both key columns are always preserved and users should
+                perform explicit post-processing if desired.
             join_keys: Tuple of two lists of column names to join on. [Deprecated]
 
         Returns: