sql: support backslash commands with python

[dbist]

Is your feature request related to a problem? Please describe.
Passing backslash commands through sqlmagic which in turn uses pgspecial library throws error

cockroachdb://maxroach:***@roach-0:26257/movr?sslcert=/certs/client.maxroach.crt&sslkey=/certs/client.maxroach.key&sslmode=verify-full&sslrootcert=/certs/ca.crt
   cockroachdb://maxroach@roach-0:26257/movr?sslcert=/certs/client.maxroach.crt&sslkey=/certs/client.maxroach.key&sslmode=verify-full&sslrootcert=/certs/ca.crt
(psycopg2.errors.SyntaxError) at or near "\": syntax error
DETAIL:  source SQL:
\\dt
^
[SQL: \\dt]
(Background on this error at: http://sqlalche.me/e/f405)

See thread https://cockroachlabs.slack.com/archives/CPD3ANLMB/p1584468085091500

Describe the solution you'd like
Passing \dt or \?, etc, commands should result in intended CLI output.

Here's the package in question: https://pypi.org/project/pgspecial/

[awoods187]

@rafiss this was one of the sqlalchemy related items

[rafiss]

The problem seems to be this if-statement in ipython-sql:

            if first_word.startswith('\\') and 'postgres' in str(conn.dialect):
                if not PGSpecial:
                    raise ImportError('pgspecial not installed')
                pgspecial = PGSpecial()

https://github.com/catherinedevlin/ipython-sql/blob/ad79dd7bbb07a9a5f0a61ba2758295d7d5d0c9b2/src/sql/run.py#L354

It will only use pgspecial if postgres is part of the connection string. But in order to connect to CockroachDB, the connection string must begin with cockroachdb.

[RoachietheSupportRoach]

Zendesk ticket #5293 has been linked to this issue.

[rafiss]

Closing, since this requires a fix in the ipython-sql project.