ahirner opened a new issue, #10935:
URL: https://github.com/apache/datafusion/issues/10935
### Is your feature request related to a problem or challenge?
Currently where clauses in a sub query are not pushed below `Unnest`
expressions. In conjunction with some other limitations, it composing views
with `unnest()` not ideal.
In `0.39.0` cli:
```
> CREATE TABLE IF NOT EXISTS v AS VALUES(1,[1,2,3]),(2,[3,4,5]);
0 row(s) fetched.
Elapsed 0.008 seconds.
```
We get equal results with or w/o a subquery:
```
> select unnest(column2) from v where column1=2;
+-------------------+
| unnest(v.column2) |
+-------------------+
| 3 |
| 4 |
| 5 |
+-------------------+
3 row(s) fetched.
Elapsed 0.011 seconds.
```
```
> select "unnest(v.column2)" from (select unnest(column2), column1 from v)
where column1=2;
+-------------------+
| unnest(v.column2) |
+-------------------+
| 3 |
| 4 |
| 5 |
+-------------------+
3 row(s) fetched.
Elapsed 0.015 seconds.
```
`Filter` and `FilterExec` are above projections with `unnest`, instead of
below.
Ok:
```
> explain select unnest(column2) from v where column1=2;
+---------------+------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+------------------------------------------------------------------------+
| logical_plan | Unnest: lists[unnest(v.column2)] structs[]
|
| | Projection: v.column2 AS unnest(v.column2)
|
| | Filter: v.column1 = Int64(2)
|
| | TableScan: v projection=[column1, column2]
|
| physical_plan | UnnestExec
|
| | RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1 |
| | ProjectionExec: expr=[column2@1 as unnest(v.column2)]
|
| | CoalesceBatchesExec: target_batch_size=8192
|
| | FilterExec: column1@0 = 2
|
| | MemoryExec: partitions=1, partition_sizes=[1]
|
| |
|
+---------------+------------------------------------------------------------------------+
```
Problematic:
```
> explain select "unnest(v.column2)" from (select unnest(column2), column1
from v) where column1=2;
+---------------+---------------------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+---------------------------------------------------------------------------------------+
| logical_plan | Projection: unnest(v.column2)
|
| | Filter: v.column1 = Int64(2)
|
| | Unnest: lists[unnest(v.column2)] structs[]
|
| | Projection: v.column2 AS unnest(v.column2),
v.column1 |
| | TableScan: v projection=[column1, column2]
|
| physical_plan | ProjectionExec: expr=[unnest(v.column2)@0 as
unnest(v.column2)] |
| | CoalesceBatchesExec: target_batch_size=8192
|
| | FilterExec: column1@1 = 2
|
| | RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1 |
| | UnnestExec
|
| | ProjectionExec: expr=[column2@1 as
unnest(v.column2), column1@0 as column1] |
| | MemoryExec: partitions=1, partition_sizes=[1]
|
| |
|
+---------------+---------------------------------------------------------------------------------------+
```
### Describe the solution you'd like
`FilterExec` is pushed down to tables that support them.
### Describe alternatives you've considered
A workaround is trying to not use subqueries. However, then one cannot unest
structs with multiple lists, or unnest a column more than once. Those are also
unsupported.
```
> select unnest(unnest([[1],[1,2],[1,2,3]]));
type_coercion
caused by
This feature is not implemented: Unnest should be rewritten to
LogicalPlan::Unnest before type coercion
```
```
> select unnest(column2) as x, unnest(column2) as y from v;
Error during planning: Projections require unique expression names but the
expression "v.column2 AS unnest(v.column2)" at position 0 and "v.column2 AS
unnest(v.column2)" at position 1 have the same name. Consider aliasing ("AS")
one of them.
```
(note: a real case would be something like `select
unnest(named_struct)['foo'] as foo, unnest(named_struct)['bar'] as bar`).
### Additional context
Maybe related: #5364
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