HeartSaVioR commented on code in PR #40561:
URL: https://github.com/apache/spark/pull/40561#discussion_r1160967676


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python/pyspark/sql/dataframe.py:
##########
@@ -3928,6 +3928,71 @@ def dropDuplicates(self, subset: Optional[List[str]] = 
None) -> "DataFrame":
             jdf = self._jdf.dropDuplicates(self._jseq(subset))
         return DataFrame(jdf, self.sparkSession)
 
+    def dropDuplicatesWithinWatermark(self, subset: Optional[List[str]] = 
None) -> "DataFrame":
+        """Return a new :class:`DataFrame` with duplicate rows removed,
+         optionally only considering certain columns, within watermark.
+
+        For a static batch :class:`DataFrame`, it just drops duplicate rows. 
For a streaming
+        :class:`DataFrame`, this will keep all data across triggers as 
intermediate state to drop
+        duplicated rows. The state will be kept to guarantee the semantic, 
"Events are deduplicated
+        as long as the time distance of earliest and latest events are smaller 
than the delay
+        threshold of watermark." The watermark for the input 
:class:`DataFrame` must be set via
+        :func:`withWatermark`. Users are encouraged to set the delay threshold 
of watermark longer

Review Comment:
   If we want to support this API in batch query, I think we have to implement 
the same behavior, not forwarding to dropDuplicates(). But that's also very odd 
because we are telling users that watermark is no-op in batch query and now we 
have to get delay threshold from withWatermark. I'd say it conflicts with base 
concept.



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