zhengruifeng commented on PR #39462:
URL: https://github.com/apache/spark/pull/39462#issuecomment-1375295176

   the duplicated names will be supported after 
https://github.com/apache/spark/pull/39461 get merged.
   
   
   but for duplicated field names in nested struct like. 
`df.select(F.struct("a", "a"))`
   
   it works in PySpark
   ```
   [Row(struct(a, a)=Row(a=1, a=1)),
    Row(struct(a, a)=Row(a=2, a=2)),
    Row(struct(a, a)=Row(a=3, a=3))]
   ```
   
   but fails in `RecordBatchReader.read_next_batch`:
   ```
   ERROR [0.583s]: test_collect_nested_type 
(pyspark.sql.tests.connect.test_connect_basic.SparkConnectBasicTests)
   ----------------------------------------------------------------------
   Traceback (most recent call last):
     File 
"/Users/ruifeng.zheng/Dev/spark/python/pyspark/sql/tests/connect/test_connect_basic.py",
 line 2038, in test_collect_nested_type
       cdf.select(CF.struct("a", "a")).collect(),
     File 
"/Users/ruifeng.zheng/Dev/spark/python/pyspark/sql/connect/dataframe.py", line 
1148, in collect
       table = self._session.client.to_table(query)
     File 
"/Users/ruifeng.zheng/Dev/spark/python/pyspark/sql/connect/client.py", line 
415, in to_table
       table, _ = self._execute_and_fetch(req)
     File 
"/Users/ruifeng.zheng/Dev/spark/python/pyspark/sql/connect/client.py", line 
589, in _execute_and_fetch
       for batch in reader:
     File "pyarrow/ipc.pxi", line 638, in __iter__
     File "pyarrow/ipc.pxi", line 674, in 
pyarrow.lib.RecordBatchReader.read_next_batch
     File "pyarrow/error.pxi", line 100, in pyarrow.lib.check_status
   pyarrow.lib.ArrowInvalid: Ran out of field metadata, likely malformed
   ```
   
   seems duplicated fields names are not allowed in `RecordBatchReader`.
   
   The only approach I can image is to:
   1,  in the server side: check the deduplicated names and modify the schema 
if necessary;
   2, in the client side: convert the schema back after fetch the arrow data.
   
   


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