Impossible to select arbitrary column when using SQLAlchemy

• asyncpg version: asyncpg==0.21.0
• PostgreSQL version: 13
• Python version: 3.6
• Platform: Alpine Linux (3.8)
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?: N/A
• Can the issue be reproduced under both asyncio and
  uvloop?: I don't know, I'm using uvloop right now

I'm trying to use asyncpg with SQLAlchemy on a project of mine. However, the following constructs to select a subset of columns in the underlying table doesn't work:

query = mytable.select(mytable.c.date)
results = await database.fetch_all(query)

This raises the following error:

  File "./main.py", line 140, in post_telemetry
    tel_results = await vmo.database.fetch_all(tel_query)
  File "/usr/local/lib/python3.6/site-packages/databases/core.py", line 140, in fetch_all
    return await connection.fetch_all(query, values)
  File "/usr/local/lib/python3.6/site-packages/databases/core.py", line 239, in fetch_all
    return await self._connection.fetch_all(built_query)
  File "/usr/local/lib/python3.6/site-packages/databases/backends/postgres.py", line 160, in fetch_all
    rows = await self._connection.fetch(query, *args)
  File "/usr/local/lib/python3.6/site-packages/asyncpg/connection.py", line 443, in fetch
    return await self._execute(query, args, 0, timeout)
  File "/usr/local/lib/python3.6/site-packages/asyncpg/connection.py", line 1446, in _execute
    query, args, limit, timeout, return_status=return_status)
  File "/usr/local/lib/python3.6/site-packages/asyncpg/connection.py", line 1454, in __execute
    return await self._do_execute(query, executor, timeout)
  File "/usr/local/lib/python3.6/site-packages/asyncpg/connection.py", line 1466, in _do_execute
    stmt = await self._get_statement(query, None)
  File "/usr/local/lib/python3.6/site-packages/asyncpg/connection.py", line 351, in _get_statement
    statement = await self._protocol.prepare(stmt_name, query, timeout)
  File "asyncpg/protocol/protocol.pyx", line 163, in prepare
asyncpg.exceptions.DatatypeMismatchError: argument of AND must be type boolean, not type timestamp with time zone

As far as I can't tell, asyncpg doesn't seem to support this feature that is present in SQLAlchemy since version 1.4, but I may be wrong.

Let me know if you need additional information.

Beginne damit, die SQLAlchemy-Abfrage zur Spaltenauswahl mit den gemeldeten Versionen von Python, PostgreSQL und den Paketen zu reproduzieren, und untersuche anschließend das über databases an asyncpg übergebene SQL. Bestätige, ob die generierte Abfrage den Datentypkonfliktfehler verursacht; abgeschlossen ist die Aufgabe, wenn das Auswählen einer Teilmenge von Spalten erfolgreich ausgeführt wird.