Unused unnested column is not pruned

Describe the bug

When a column from a UnnestExec is not used, it is not removed

To Reproduce

Run datafusion-cli against this query:

CREATE TABLE test_table (
    id INT,
    value INT
) AS VALUES (1, 100), (2, 200), (3, 300);

EXPLAIN SELECT id
FROM (
    SELECT id, UNNEST(make_array(1, 2, 3)) as elem
    FROM test_table
)
GROUP BY id;

This currently generates this plan

+---------------+-------------------------------+
| plan_type     | plan                          |
+---------------+-------------------------------+
| physical_plan | ┌───────────────────────────┐ |
|               | │       AggregateExec       │ |
|               | │    --------------------   │ |
|               | │        group_by: id       │ |
|               | │                           │ |
|               | │           mode:           │ |
|               | │      FinalPartitioned     │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │      RepartitionExec      │ |
|               | │    --------------------   │ |
|               | │ partition_count(in->out): │ |
|               | │          14 -> 14         │ |
|               | │                           │ |
|               | │    partitioning_scheme:   │ |
|               | │      Hash([id@0], 14)     │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │       AggregateExec       │ |
|               | │    --------------------   │ |
|               | │        group_by: id       │ |
|               | │       mode: Partial       │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │      RepartitionExec      │ |
|               | │    --------------------   │ |
|               | │ partition_count(in->out): │ |
|               | │          1 -> 14          │ |
|               | │                           │ |
|               | │    partitioning_scheme:   │ |
|               | │    RoundRobinBatch(14)    │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │       ProjectionExec      │ |
|               | │    --------------------   │ |
|               | │           id: id          │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │         UnnestExec        │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │       ProjectionExec      │ |
|               | │    --------------------   │ |
|               | │    __unnest_placeholder   │ |
|               | │    (make_array(Int64(1    │ |
|               | │   ),Int64(2),Int64(3))):  │ |
|               | │         [1, 2, 3]         │ |
|               | │                           │ |
|               | │           id: id          │ |
|               | └─────────────┬─────────────┘ |
|               | ┌─────────────┴─────────────┐ |
|               | │       DataSourceExec      │ |
|               | │    --------------------   │ |
|               | │         bytes: 224        │ |
|               | │       format: memory      │ |
|               | │          rows: 1          │ |
|               | └───────────────────────────┘ |
|               |                               |
+---------------+-------------------------------+

Expected behavior

I would have liked the UnnestExec to be removed entirely since it is not used further up the plan.

Additional context

No response

Inizia eseguendo la query SQL fornita con datafusion-cli e ispezionando il relativo piano fisico EXPLAIN, concentrandoti sui nodi ProjectionExec e UnnestExec. Traccia il comportamento del pruning per la colonna elem inutilizzata e verifica che il piano completato rimuova l’UnnestExec e il segnaposto dell’array non necessari, preservando l’aggregazione di id.