0lai0 commented on code in PR #3732:
URL: https://github.com/apache/datafusion-comet/pull/3732#discussion_r2971295599


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spark/src/test/resources/sql-tests/expressions/datetime/window_time.sql:
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@@ -0,0 +1,32 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+-- ConfigMatrix: parquet.enable.dictionary=false,true
+
+statement
+CREATE TABLE test_window_time(time timestamp, value int) USING parquet
+
+statement
+INSERT INTO test_window_time VALUES (timestamp('2023-01-01 12:00:00'), 1), 
(timestamp('2023-01-01 12:05:00'), 2), (timestamp('2023-01-01 12:15:00'), 3)
+
+-- basic window_time with tumbling window
+query spark_answer_only

Review Comment:
   Thanks @andygrove . I dug into this and tried enabling the config 
`spark.comet.operator.WindowExec.allowIncompatible=true`, but the test still 
fails if I remove `spark_answer_only`.
   
   The root cause might be at the expression level: Spark's `TimeWindowing` 
analyzer rule automatically expands `window()` into a` CreateNamedStruct` 
wrapped inside a `KnownNullable` expression. Since Comet doesn't currently 
support KnownNullable natively, the planner is forced to fall back to Spark 
anyway.
   
[https://github.com/search?q=repo%3Aapache%2Fspark+KnownNullable&type=code](https://github.com/search?q=repo%3Aapache%2Fspark+KnownNullable&type=code)
   
   Fully supporting native struct creation and KnownNullable would be a broader 
effort outside the scope of this PR (which focuses on 
`PreciseTimestampConversion` issue for `window_time`).
   
   Because of this, it might be better to keep `spark_answer_only` here and 
open a follow-up issue for those specific expressions. I'll make sure to update 
the inline comment to explicitly document the exact cause of the fallback for 
future reference. 
   Let me know your thoughts on this. 



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