Re: Check-out mutable functions in check constraints

On Fri, Jul 12, 2019 at 03:44:58PM +0900, Kyotaro Horiguchi wrote:
>Hello.
>
>As mentioned in the following message:
>
>https://www.postgresql.org/message-id/20190712.150527.145133646.horikyota.ntt%40gmail.com
>
>Mutable function are allowed in check constraint expressions but
>it is not right. The attached is a proposed fix for it including
>regression test.
>

I think the comment in parse_expr.c is wrong:

/*
* All SQL value functions are stable so we reject them in check
* constraint expressions.
*/
if (pstate->p_expr_kind == EXPR_KIND_CHECK_CONSTRAINT)
ereport(ERROR,
(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
errmsg("mutable functions are not allowed in check constraints")));

At first it claims SQL value functions are stable, but then rejects them
with a message that they're mutable.

Also, the other places use "cannot ..." messages:

case EXPR_KIND_COLUMN_DEFAULT:
err = _("cannot use column reference in DEFAULT expression");
break;

so maybe these new checks should use the same style.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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