decimal.InvalidOperation exception is thrown with AWS Redshift.

• asyncpg version: 0.23.0
• PostgreSQL version: PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.27314
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: AWS Redshift.
• Python version: 3.6.13
• Platform: Linux 5.0.0-23-generic #24~18.04.1-Ubuntu SMP Mon Jul 29 16:12:28 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?: no
• Can the issue be reproduced under both asyncio and
  uvloop?: no

I am trying to use asyncpg with AWS Redshift. I got an decimal.InvalidOperation exception when I try to run a simple query as follows. Is there any way to make asyncpg work with AWS Redshift? psycopg2 is working with AWS Redshift without major issue so I expect asyncpg could work with AWS Redshift also. Thank you in advance.

import asyncio
import asyncpg

async def run():
    conn = await asyncpg.connect(
        user='user', password='password', database='database', host='host')
    values = await conn.fetch('SELECT 1.0 / 0.5')
    await conn.close()

loop = asyncio.get_event_loop()
loop.run_until_complete(run())

$ python asyncpg_redshift.py
Traceback (most recent call last):
  File "asyncpg_redshift.py", line 11, in <module>
    loop.run_until_complete(run())
  File "/home/taeho/.pyenv/versions/3.6.13/lib/python3.6/asyncio/base_events.py", line 488, in run_until_complete
    return future.result()
  File "asyncpg_redshift.py", line 7, in run
    values = await conn.fetch('SELECT 1.0 / 0.5')
  File "/home/taeho/.pyenv/versions/3.6.13/envs/asyncpg/lib/python3.6/site-packages/asyncpg/connection.py", line 588, in fetch
    record_class=record_class,
  File "/home/taeho/.pyenv/versions/3.6.13/envs/asyncpg/lib/python3.6/site-packages/asyncpg/connection.py", line 1632, in _execute
    ignore_custom_codec=ignore_custom_codec,
  File "/home/taeho/.pyenv/versions/3.6.13/envs/asyncpg/lib/python3.6/site-packages/asyncpg/connection.py", line 1655, in __execute
    ignore_custom_codec=ignore_custom_codec,
  File "/home/taeho/.pyenv/versions/3.6.13/envs/asyncpg/lib/python3.6/site-packages/asyncpg/connection.py", line 1697, in _do_execute
    result = await executor(stmt, None)
  File "asyncpg/protocol/protocol.pyx", line 201, in bind_execute
  File "asyncpg/protocol/coreproto.pyx", line 70, in asyncpg.protocol.protocol.CoreProtocol._read_server_messages
  File "asyncpg/protocol/coreproto.pyx", line 212, in asyncpg.protocol.protocol.CoreProtocol._process__bind_execute
  File "asyncpg/protocol/coreproto.pyx", line 497, in asyncpg.protocol.protocol.CoreProtocol._parse_data_msgs
  File "asyncpg/protocol/protocol.pyx", line 781, in asyncpg.protocol.protocol.BaseProtocol._decode_row
  File "asyncpg/protocol/prepared_stmt.pyx", line 295, in asyncpg.protocol.protocol.PreparedStatementState._decode_row
  File "asyncpg/protocol/codecs/base.pyx", line 289, in asyncpg.protocol.protocol.Codec.decode
  File "asyncpg/protocol/codecs/base.pyx", line 196, in asyncpg.protocol.protocol.Codec.decode_scalar
  File "asyncpg/pgproto/./codecs/numeric.pyx", line 287, in asyncpg.pgproto.pgproto.numeric_decode_binary
  File "asyncpg/pgproto/./codecs/numeric.pyx", line 279, in asyncpg.pgproto.pgproto.numeric_decode_binary_ex
decimal.InvalidOperation: [<class 'decimal.ConversionSyntax'>]
$

I think the strange result of the following query could be also related.

import asyncio
import asyncpg

async def run():
    conn = await asyncpg.connect(
        user='user', password='password', database='database', host='host')
    values = await conn.fetch('SELECT CAST(1.0 AS DECIMAL(10, 1))')
    print(values)
    await conn.close()

loop = asyncio.get_event_loop()
loop.run_until_complete(run())

$ python asyncpg_redshift2.py
[<Record numeric=Decimal('100000.00')>]
$ 

まず、提供されている2つの Python クエリを AWS Redshift に対して実行し、その結果を traceback と比較します。数値のデコード中に失敗が発生する asyncpg/pgproto/./codecs/numeric.pyx を調査し、Redshift から返される数値データが PostgreSQL の想定する表現とどのように異なるのかを特定します。非互換性を再現し、サポート対象の動作または範囲を限定した修正を確立できれば完了です。