Fix COPY TO does not produce an output file for the empty set #18074
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| // Single-file output requires creating at least one file stream in advance. | ||
| // If no record batches are present in the input stream (zero-row scenario), |
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I think there might a bit missing from this comment. Sentence doesn't seem complete.
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rephrased it. Last sentence was indeed not complete.
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…ed test to validate schema is correct)
alamb
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Thank you @bert-beyondloops 🙏
The behavior of writing empty files has come up several times before and I worry we will go back and forth on the implementation if we don't have the expected results written down somewhere
Could you also please add some documentation to the top of this module / the demuxer tasks to make it clearer what behavior is expected?
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I've added documentation clarifying the minimum number of files written for each output scenario. |
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| /// be written with the extension from the path. Otherwise the default extension | ||
| /// will be used and the output will be split into multiple files. | ||
| /// | ||
| /// Output file guarantees: |
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Which issue does this PR close?
COPY TO does not produce a single output file for an empty set
Rationale for this change
Executing following sql does not effectively create a single output file on disk :
COPY (SELECT 1 AS id WHERE FALSE) TO 'table_no_rows.parquet';
I would expect it creates a parquet file containing 0 rows including the schema metadata.
The fact you can still query the schema of such a table is still valuable information.
What changes are included in this PR?
Are these changes tested?
Additional COPY TO test added in the copy.slt sqllogictests
Are there any user-facing changes?
A file containing 0 rows will be created now