Support for query results of type Nothing and UUID regressed in 3.0.0

[meastham]

Describe what's wrong

Queries with Nothing/UUID (and possibly other) types fail in 3.0.0 but were working in 2.x.

repro.py:

from chdb import dbapi
import traceback

conn = dbapi.connect()
cursor = conn.cursor()
for query in [
    "SELECT '6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b'::UUID",
    "SELECT NULL",
]:
    print(f"Query: {query}")
    try:
        cursor.execute(query)
        print(f"success: {cursor.fetchone()}")
    except Exception as e:
        print(f"failure:\n{traceback.format_exc()}")
    print()

Works fine with 2.x:

❯ uv run --python 3.12 --with chdb==2.1.1 repro.py
Query: SELECT '6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b'::UUID
success: ('6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b',)

Query: SELECT NULL
success: (None,)

Fails in 3.0.0:

uv run --python 3.12 --with chdb==3.0.0 repro.py
Query: SELECT '6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b'::UUID
failure:
Traceback (most recent call last):
  File "/Users/meastham/repro/repro.py", line 12, in <module>
    cursor.execute(query)
  File "/Users/meastham/.cache/uv/archive-v0/z1U-_q0CjtEXfAWREwnsj/lib/python3.12/site-packages/chdb/dbapi/cursors.py", line 132, in execute
    self._cursor.execute(query)
  File "/Users/meastham/.cache/uv/archive-v0/z1U-_q0CjtEXfAWREwnsj/lib/python3.12/site-packages/chdb/state/sqlitelike.py", line 46, in execute
    raise Exception(self._cursor.error_message())
Exception: Code: 50. DB::Exception: Code: 50. DB::Exception: The type 'UUID' of a column 'CAST('6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b', 'UUID')' is not supported for conversion into Arrow data format. (UNKNOWN_TYPE) (version 24.8.4.1). (UNKNOWN_TYPE)


Query: SELECT NULL
failure:
Traceback (most recent call last):
  File "/Users/meastham/repro/repro.py", line 12, in <module>
    cursor.execute(query)
  File "/Users/meastham/.cache/uv/archive-v0/z1U-_q0CjtEXfAWREwnsj/lib/python3.12/site-packages/chdb/dbapi/cursors.py", line 132, in execute
    self._cursor.execute(query)
  File "/Users/meastham/.cache/uv/archive-v0/z1U-_q0CjtEXfAWREwnsj/lib/python3.12/site-packages/chdb/state/sqlitelike.py", line 46, in execute
    raise Exception(self._cursor.error_message())
Exception: Code: 50. DB::Exception: Code: 50. DB::Exception: The type 'Nothing' of a column 'NULL' is not supported for conversion into Arrow data format. (UNKNOWN_TYPE) (version 24.8.4.1). (UNKNOWN_TYPE)

Does it reproduce on the most recent release?

Yes

Expected behavior

I expect these queries to succeed

[meastham]

I originally repro'd this on MacOS 15.2 but it also happens on Linux:

❯ docker run --rm -it -v .:/tmp/repro ghcr.io/astral-sh/uv:debian uv run --python 3.12 --with chdb==3.0.0 /tmp/repro/repro.py
Installed 8 packages in 49ms
Query: SELECT '6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b'::UUID
failure:
Traceback (most recent call last):
  File "/tmp/repro/repro.py", line 12, in <module>
    cursor.execute(query)
  File "/root/.cache/uv/archive-v0/mobp6VEk6iq7wxUmoCwYi/lib/python3.12/site-packages/chdb/dbapi/cursors.py", line 132, in execute
    self._cursor.execute(query)
  File "/root/.cache/uv/archive-v0/mobp6VEk6iq7wxUmoCwYi/lib/python3.12/site-packages/chdb/state/sqlitelike.py", line 46, in execute
    raise Exception(self._cursor.error_message())
Exception: Code: 50. DB::Exception: Code: 50. DB::Exception: The type 'UUID' of a column 'CAST('6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b', 'UUID')' is not supported for conversion into Arrow data format. (UNKNOWN_TYPE) (version 24.8.4.1). (UNKNOWN_TYPE)


Query: SELECT NULL
failure:
Traceback (most recent call last):
  File "/tmp/repro/repro.py", line 12, in <module>
    cursor.execute(query)
  File "/root/.cache/uv/archive-v0/mobp6VEk6iq7wxUmoCwYi/lib/python3.12/site-packages/chdb/dbapi/cursors.py", line 132, in execute
    self._cursor.execute(query)
  File "/root/.cache/uv/archive-v0/mobp6VEk6iq7wxUmoCwYi/lib/python3.12/site-packages/chdb/state/sqlitelike.py", line 46, in execute
    raise Exception(self._cursor.error_message())
Exception: Code: 50. DB::Exception: Code: 50. DB::Exception: The type 'Nothing' of a column 'NULL' is not supported for conversion into Arrow data format. (UNKNOWN_TYPE) (version 24.8.4.1). (UNKNOWN_TYPE)

[auxten]

cursor.execute is using ArrowStream as internal type to impl the fetchone and fetchall.
But ArrowStream do not have complete types. This is a problem chDB should solve.

For now, you can use connect.query to work around this type issue like:
SELECT '6bbd51ac-b0cc-43a2-8cb2-eab06ff7de7b'::UUID