Nithurshen opened a new pull request, #18987:
URL: https://github.com/apache/datafusion/pull/18987
## Which issue does this PR close?
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- Closes #16280
## Rationale for this change
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Why are you proposing this change? If this is already explained clearly in
the issue then this section is not needed.
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Substrait roundtrip tests were failing for queries involving `EXISTS` and
correlated subqueries (specifically those using outer references). The
DataFusion Substrait producer did not support serializing `Expr::Exists`, and
it threw a "feature not implemented" error for `OuterReferenceColumn`.
Supporting these features is essential for improving the reliability of
DataFusion's Substrait integration and enabling complex join scenarios in
distributed environments.
## What changes are included in this PR?
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sometimes worth providing a summary of the individual changes in this PR.
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1. **Producer Support for `EXISTS`:**
* Implemented `from_exists` in the producer to map `Expr::Exists` to the
Substrait `SetPredicate` (using `PredicateOp::Existence`).
* Added support for `NOT EXISTS` by wrapping the predicate in a "not"
scalar function.
2. **Producer Support for `OuterReferenceColumn`:**
* Updated the producer to serialize `OuterReferenceColumn` as a custom
scalar function named `"outer_reference"`. This avoids schema validation errors
during serialization since outer columns often cannot be resolved against the
local subquery schema.
3. **Consumer Support for `OuterReferenceColumn`:**
* Updated the consumer to intercept the `"outer_reference"` scalar
function and deserialize it back into a DataFusion `OuterReferenceColumn`,
ensuring a successful roundtrip.
## Are these changes tested?
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Yes.
* Verified using the existing SQLLogicTest case that was previously failing:
`joins.slt`.
* Command run: `cargo test --test sqllogictests -- --substrait-round-trip
joins.slt:1233`
## Are there any user-facing changes?
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No breaking API changes. This PR purely expands the coverage of supported
Logical Plans that can be converted to/from Substrait.
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