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chore: fix compatibility guide #978

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kazuyukitanimura merged 1 commit into from
Sep 27, 2024
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chore: fix compatibility guide #978

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8 changes: 8 additions & 0 deletions docs/templates/compatibility-template.md
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Expand Up @@ -38,6 +38,14 @@ Comet uses the Rust regexp crate for evaluating regular expressions, and this ha
regular expression engine. Comet will fall back to Spark for patterns that are known to produce different results, but
this can be overridden by setting `spark.comet.regexp.allowIncompatible=true`.

## Floating number comparison

Spark normalizes NaN and zero for floating point numbers for several cases. See `NormalizeFloatingNumbers` optimization rule in Spark.
However, one exception is comparison. Spark does not normalize NaN and zero when comparing values
because they are handled well in Spark (e.g., `SQLOrderingUtil.compareFloats`). But the comparison
functions of arrow-rs used by DataFusion do not normalize NaN and zero (e.g., [arrow::compute::kernels::cmp::eq](https://docs.rs/arrow/latest/arrow/compute/kernels/cmp/fn.eq.html#)).
So Comet will add additional normalization expression of NaN and zero for comparison.
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@viirya viirya Sep 27, 2024

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Oh, I added this to docs/source/user-guide/compatibility.md.


## Cast

Cast operations in Comet fall into three levels of support:
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