[substrait] [sqllogictest] Cannot convert <subquery> to Substrait

[gabotechs]

Describe the bug

~30 sqllogictest cases are failing in Substrait round-trip mode because of the following error:

query failed: DataFusion error: This feature is not implemented: Cannot convert <subquery> to Substrait

To Reproduce

cargo test --test sqllogictests -- --substrait-round-trip subquery.slt:1007

Expected behavior

The sqllogictest passes in Substrait round-trip mode

Additional context

This is part of a broader initiative to improve the reliability of Substrait-to-DataFusion logical plan conversions.

• [Epic] A collection of Substrait conversion issues #16248

[ViggoC]

take

[ViggoC]

Hi @gabotechs, I'm trying to fix cargo test --test sqllogictests -- --substrait-round-trip subquery.slt:1007, and handle converting OuterReferenceColumn is necessary to do it. But I found following description in #8149，what does it mean?

The following exprs I think we don't need to support:
OuterReferenceColumn
Placeholder

[gabotechs]

🤔 I'm not very familiar with that, the issue looks relatively old and things might have changed since then.

If you manage to make it work adding support for OuterReferenceColumn, probably things would become clearer in the actual PR.