ARROW-10163: [Rust] [DataFusion] Add DictionaryArray coercion support to physical plans #8359
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alamb
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Oct 6, 2020
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FWIW I don't understand why order_coercion and eq_coercion are different (eq_coercion does not include string_coercion).
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As in #8340, I don't think partially redundant and incomplete checks for casting support in DataFusion adds much over the actual arrow casting, so I have removed the plan time checks
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Unrelated to this PR, I just renamed some of these arguments to match the comment description
rust/datafusion/tests/sql.rs
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here is the (simple) end to end test for DictionaryArray support
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NOTE: this builds on #8346 so leaving as a draft until those are merged
This PR adds basic physical expression / casting support to DataFusion. Right now, it will cause all
DictionaryArraydata to be unpacked into aStringArrayfor operations.Ideally, DataFusion would support direct comparison / operation on DictionaryArrays, however, there isn't the necessary support in the arrow kernels yet to do so (e.g. there is no Dictionary equality comparison kernel I could find https://github.com/apache/arrow/blob/master/rust/arrow/src/compute/kernels/comparison.rs
However, this PR gets the basic queries running and I hope to contribute further optimizations as time allows and our project needs dictate.