Proposal: Include CHECK constraint expression in violation error DETAIL

Hi,

When a CHECK constraint is violated, PostgreSQL reports the constraint name
and the failing row, but not the constraint expression:

ERROR: new row for relation "staff_sales" violates check constraint "staff_age_check"
DETAIL: Failing row contains (1, 15).

Users need to inspect the table with \d to find the violated condition.
Is there a reason why the expression is not included in the error detail?
(For example, having such information appear in logs could pose a
security risk.)

Including it in DETAIL would avoid this extra step:

DETAIL: Failing row contains (1, 15). Check constraint expression: (age >= 18).

I have attached a concept patch to illustrate the idea. Please note that
this is a work in progress.

For the implementation, I wrote the expression generation by referring to
pg_get_constraintdef_worker().

Regarding security, I have not yet added any permission checks. I plan to
investigate whether they are needed at all, and if so what form they should
take, using the existing handling of the failing-row detail and the
previous proposal that was already committed as references:
<https://www.postgresql.org/message-id/flat/9f9dc7ae-14f0-4a25-5485-964d9bfc19bd%40lab.ntt.co.jp>

If this proposal is considered worthwhile, I would like to continue
developing the patch myself.

Regards,

Taiki Koshino<koshino(at)sraoss(dot)co(dot)jp>
SRA OSS K.K.
TEL: 03-5979-2701 FAX: 03-5979-2702
URL: https://www.sraoss.co.jp/