Subject: psycopg3 - parameters cannot be used for DDL commands?

From: Les <[email-masked]>
Date: Wed, 5 Jan 2022 17:42:31 +0100

Example:

Traceback (most recent call last):
  File "/usr/sbin/prepare_postgres", line 46, in <module>
    pg_exec_postgres("ALTER USER postgres WITH PASSWORD %s",
[POSTGRES_PASSWORD])
  File "/opt/util.py", line 101, in pg_exec_postgres
    return pg_conn_postgres().execute(*args, **kwargs)
  File "/usr/local/lib/python3.9/dist-packages/psycopg/connection.py", line
722, in execute
    raise ex.with_traceback(None)
psycopg.errors.SyntaxError: syntax error at or near "$1"
LINE 1: ALTER USER postgres WITH PASSWORD $1
                                          ^
PostgreSQL server log:

2022-01-05 17:35:25.831 CET [58] ERROR:  syntax error at or near "$1" at
character 35
2022-01-05 17:35:25.831 CET [58] STATEMENT:  ALTER USER postgres WITH
PASSWORD $1

Passwords can also contain special characters. If I can't use parameters to
do this, then how should I quote them in a safe way?

Thank you,

   Laszlo

---

From: Tom Lane <[email-masked]>
Date: Wed, 05 Jan 2022 12:07:47 -0500

> 2022-01-05 17:35:25.831 CET [58] STATEMENT:  ALTER USER postgres WITH

Yeah, as a general rule parameters can only be used in DML commands
(SELECT/INSERT/UPDATE/DELETE).  Utility commands don't support them
because they don't have expression-evaluation capability.

(Perhaps this will change someday, but don't hold your breath.)

> do this, then how should I quote them in a safe way?

Most client libraries should have a function to convert an arbitrary
string into a safely-quoted SQL literal that you can embed into the
command.  I don't know psycopg3, so I don't know what it has for that.

			regards, tom lane

---

From: Les <[email-masked]>
Date: Wed, 5 Jan 2022 18:19:12 +0100

Ok, thanks!

---

From: Dmitry Igrishin <[email-masked]>
Date: Wed, 5 Jan 2022 20:20:36 +0300

> command.  I don't know psycopg3, so I don't know what it has for that.
My C++ library, - Pgfe, - can convert any named parameter into an
arbitrary part of SQL expression by using Sql_string::replace()
method. For example:
  update :foo
could be replaced to
  update foo set bar = 'baz' where id = 1
by using
  s.replace("foo", R"(set bar='baz' where id = 1)").

---

From: Les <[email-masked]>
Date: Wed, 5 Jan 2022 18:28:37 +0100

Well okay, I'm obviously using python. psycopg3 does not have an escape
function, they try to avoid this at all costs.

Actually their documentation is very funny, at
https://www.psycopg.org/psycopg3/docs/basic/params.html there are these
warnings:

   -

   Don’t manually merge values to a query: hackers from a foreign country
   will break into your computer and steal not only your disks, but also your
   cds, leaving you only with the three most embarrassing records you ever
   bought. On cassette tapes.
   -

   If you use the % operator to merge values to a query, con artists will
   seduce your cat, who will run away taking your credit card and your
   sunglasses with them.
   -

   If you use + to merge a textual value to a string, bad guys in balaclava
   will find their way to your fridge, drink all your beer, and leave your
   toilet sit up and your toilet paper in the wrong orientation.
   -

   You don’t want to manually merge values to a query: use the provided
   methods
   <https://www.psycopg.org/psycopg3/docs/basic/params.html#query-parameters>
   instead.

I think I'll open an issue because it looks like manual string quoting
cannot be avoided in some cases.

   Laszlo

Dmitry Igrishin <[email-masked]> ezt írta (időpont: 2022. jan. 5., Sze,

---

From: Les <[email-masked]>
Date: Thu, 6 Jan 2022 10:37:20 +0100

Okay I was wrong. I just did not know that it existed in psycopg3.

There is "client side binding":
https://www.psycopg.org/psycopg3/docs/basic/from_pg2.html#server-side-binding

from psycopg import sqlconn.execute(sql.SQL("ALTER USER some_user WITH
PASSWORD {}").format(PASSWORD))

Issue was closed: https://github.com/psycopg/psycopg/issues/199

Les <[email-masked]> ezt írta (időpont: 2022. jan. 5., Sze, 18:28):

>    If you use + to merge a textual value to a string, bad guys in
>    balaclava will find their way to your fridge, drink all your beer, and
>    leave your toilet sit up and your toilet paper in the wrong orientation.
>    -
>
> Dmitry Igrishin <[email-masked]> ezt írta (időpont: 2022. jan. 5.,
> Sze, 18:19):
>