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Posted to github@datafusion.apache.org by "Fly-a-Kite (via GitHub)" <gi...@apache.org> on 2026/05/27 02:42:31 UTC

[I] DISTINCT ORDER BY NULLS FIRST LIMIT returns the wrong top row [datafusion]

Fly-a-Kite opened a new issue, #22554:
URL: https://github.com/apache/datafusion/issues/22554

   ### Describe the bug
   
   `SELECT DISTINCT v FROM t0 ORDER BY v ASC NULLS FIRST LIMIT 1` should return
   the first row of the same ordered `DISTINCT` query without `LIMIT`. On
   DataFusion `53.0.0`, the full ordered query puts `NULL` first, but adding
   `LIMIT 1` returns the first non-null value for string, integer, and float
   columns.
   
   ### To Reproduce
   
   ## Environment
   ```text
    OS: Ubuntu 24.04.1 x86_64
    Python: 3.12.3
    datafusion: 53.0.0
    pyarrow: 24.0.0
   ```
   ## Reproduce
   ```python
   import pyarrow as pa
   from datafusion import SessionContext
   
   ctx = SessionContext()
   batch = pa.RecordBatch.from_pylist(
       [{"v": None}, {"v": ""}, {"v": "a"}],
       schema=pa.schema([pa.field("v", pa.string(), nullable=True)]),
   )
   ctx.register_record_batches("t0", [[batch]])
   
   full_sql = "SELECT DISTINCT v FROM t0 ORDER BY v ASC NULLS FIRST"
   top1_sql = full_sql + " LIMIT 1"
   
   full = ctx.sql(full_sql).collect()[0].to_pydict()["v"]
   top1 = ctx.sql(top1_sql).collect()[0].to_pydict()["v"]
   
   print("full:", full)
   print("top1:", top1)
   assert top1 == full[:1]
   ```
   
   ## Output
   ```text
   full: [None, '', 'a']
   top1: [None]
   ```
   
   ### Expected behavior
   
   ```text
   full: [None, '', 'a']
   top1: ['']
   ```
   
   ### Additional context
   
   _No response_


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Re: [I] DISTINCT ORDER BY NULLS FIRST LIMIT returns the wrong top row [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #22554:
URL: https://github.com/apache/datafusion/issues/22554#issuecomment-4557377303

   > [@alamb](https://github.com/alamb) is this another regression of the same kind?
   
   Yes I think so -- added to the release tickets


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Re: [I] DISTINCT ORDER BY NULLS FIRST LIMIT returns the wrong top row [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #22554: DISTINCT ORDER BY NULLS FIRST LIMIT returns the wrong top row
URL: https://github.com/apache/datafusion/issues/22554


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Re: [I] DISTINCT ORDER BY NULLS FIRST LIMIT returns the wrong top row [datafusion]

Posted by "kumarUjjawal (via GitHub)" <gi...@apache.org>.
kumarUjjawal commented on issue #22554:
URL: https://github.com/apache/datafusion/issues/22554#issuecomment-4553593442

   @alamb is this another regression of the same kind?


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