EXPLAIN output contains insufficient information to understand types

[findepi]

For example:

> explain select a as c from (VALUES (NULL), (NULL), (NULL)) as T(a);
+---------------+---------------------------------------+
| plan_type     | plan                                  |
+---------------+---------------------------------------+
| logical_plan  | Projection: t.a AS c                  |
|               |   SubqueryAlias: t                    |
|               |     Projection: column1 AS a          |
|               |       Values: (NULL), (NULL), (NULL)  |
| physical_plan | ProjectionExec: expr=[column1@0 as c] |
|               |   ValuesExec                          |
|               |                                       |
+---------------+---------------------------------------+

from the output one could assume the type of a to be Null, but it used to be Utf8 eg in in DF v40, as can be seen using arrow_typeof

> select arrow_typeof(a) as c from (VALUES (NULL), (NULL), (NULL)) as T(a);
+------+
| c    |
+------+
| Utf8 |
| Utf8 |
| Utf8 |
+------+

Using arrow_typeof should not be needed to reason about EXPLAIN plans.

[findepi]

Using arrow_typeof should not be needed to reason about EXPLAIN plans.

It's not.

This is my mistake. i checked EXPLAIN plan from latest DF, but mistakenly arrow_typeof output was from a different version. No surprise they didn't quite match.

[alamb]

I think you can get this information with EXPLAIN VERBOSE already:

For example,

> explain verbose select * from values (1);
....
|                                                            |                                                                                     |
| physical_plan_with_schema                                  | ValuesExec, schema=[column1:Int64;N]                                                |
|                                                            |                                                                                     |

Maybe we should improve the documentation in this area