Michael-J-Ward commented on issue #589:
URL:
https://github.com/apache/datafusion-python/issues/589#issuecomment-2176155939
`ctx.sql(..)` returns a `PyDataFrame`, and then you are observing the python
shell call `PyDataFrame::__repr__` to print it out, which applies a `LIMIT` and
collects the first 10 rows.
If you were to assign it and then collect, you'd see the proper result.
```python
>>> df = ctx.sql("explain select 1")
>>> df.collect()
[pyarrow.RecordBatch
plan_type: string not null
plan: string not null
----
plan_type: ["logical_plan","physical_plan"]
plan: ["Projection: Int64(1)
EmptyRelation","ProjectionExec: expr=[1 as Int64(1)]
PlaceholderRowExec
"]]
```
And then here's the error reproduced with a little more detail.
```python
>>> df = ctx.sql("explain select 1")
>>> # we can print the (unsupported) logical plan - notice `EXPLAIN` is not
the top row of the plan
>>> df.limit(count=10, offset=0).explain()
DataFrame()
+--------------+--------------------------+
| plan_type | plan |
+--------------+--------------------------+
| logical_plan | Limit: skip=0, fetch=10 |
| | Explain |
| | Projection: Int64(1) |
| | EmptyRelation |
+--------------+--------------------------+
>>> # but calling collect reproduces the error
>>> df.limit(count=10, offset=0).collect()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Exception: Internal error: Unsupported logical plan: Explain must be root of
the plan.
This was likely caused by a bug in DataFusion's code and we would welcome
that you file an bug report in our issue tracker
```
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