ExpandRel output type discrepancy

[vbarua]

The protobuf comment

In addition to a field being emitted per input field an extra int64 field is emitted

Disagrees with the written spec:

The expand fields followed by an i32 column describing the index of the duplicate that the row is derived from.

We should reconcile this.

[Blizzara]

Should it be "i32 or i64 field", allowing both? At least in Spark the type of the field depends on some config option, defaulting now to i64 but earlier i32: https://github.com/apache/spark/blob/master/docs/sql-migration-guide.md#upgrading-from-spark-sql-30-to-31 (see second item).