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From: Phillip Diffley <[email protected]>
To: [email protected]
Subject: Stably escaping an identifier
Date: Sun, 15 Jun 2025 21:55:10 +0200
Message-ID: <CAGAwPgQ+rhRaiPyrjG2DZhEgtYxRnsAa6jZYq2FdHu8Se+YWdg@mail.gmail.com> (raw)

I am in a situation where I need to run dynamically generated queries with
identifiers from an untrusted source. For example
SELECT * FROM <untrusted_table_name> WHERE <untrusted_column_name> = $1;

We can use format('%I', <untrusted_value>) to escape the identifier and
avoid a security vulnerability, but if the provided identifier is already
escaped, this introduces a problem. For example,
SELECT format('%I', 'my identifier');
returns "my identifier", but
SELECT format('%I', format('%I', 'my identifier'));
returns """my identifier"""
because it is escaping the previously added quotation marks.

Is there a reliable way to determine if an identifier has already been
escaped, or alternatively is there a function that will stably escape an
identifier such that the identifier will not change if the function is
called repeatedly?

Thanks,
Phillip

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