xudong963 commented on PR #15683:
URL: https://github.com/apache/datafusion/pull/15683#issuecomment-2796589760

   I don't understand the failing sqllogictest:
   
   ```
   # Check output plan again, expect no "output_ordering" clause in the 
physical_plan -> ParquetExec,
   # due to there being more files than partitions:
   query TT
   EXPLAIN SELECT int_col, string_col
   FROM test_table
   ORDER BY string_col, int_col;
   ----
   logical_plan
   01)Sort: test_table.string_col ASC NULLS LAST, test_table.int_col ASC NULLS 
LAST
   02)--TableScan: test_table projection=[int_col, string_col]
   physical_plan
   01)SortPreservingMergeExec: [string_col@1 ASC NULLS LAST, int_col@0 ASC 
NULLS LAST]
   02)--SortExec: expr=[string_col@1 ASC NULLS LAST, int_col@0 ASC NULLS LAST], 
preserve_partitioning=[true]
   03)----DataSourceExec: file_groups={2 groups: 
[[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/parquet/test_table/0.parquet,
 
WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/parquet/test_table/1.parquet],
 
[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/parquet/test_table/2.parquet]]},
 projection=[int_col, string_col], file_type=parquet
   ```
   
   Based on current code and doc, my understanding is that the 
`output_ordering`, aka. `file_sort_order` refers to the file order, that is, if 
we specify the output_ordering, what we can ensure is that the data in a single 
file is ordered.  
https://datafusion.apache.org/user-guide/sql/ddl.html#cautions-when-using-the-with-order-clause
   
   So why `expect no "output_ordering" clause in the physical_plan -> 
ParquetExec due to there being more files than partitions`? 🤔 
   
   
   


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