Horton

Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions

jian he <jian.universality@gmail.com>

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From: jian he <jian.universality@gmail.com>
To: Vik Fearing <vik@postgresfriends.org>
Cc: Corey Huinker <corey.huinker@gmail.com>, Isaac Morland <isaac.morland@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-07-24T13:44:22Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Make cast functions to type money error safe

  2. Make cast function from circle to polygon error safe

  3. Make geometry cast functions error safe

  4. Make cast functions from jsonb error safe

  5. Make many cast functions error safe

  6. Add SQL/JSON query functions

  7. Add soft error handling to some expression nodes

On Tue, Jul 22, 2025 at 8:26 PM Vik Fearing <vik@postgresfriends.org> wrote:
>
>
> On 22/07/2025 12:19, jian he wrote:
> > On Tue, Jul 22, 2025 at 2:45 PM Vik Fearing <vik@postgresfriends.org> wrote:
> >> It was accepted into the standard after 2023 was released.  I am the
> >> author of this change in the standard, so feel free to ask me anything
> >> you're unsure about.
> >>
> > is the generally syntax as mentioned in this thread:
> > CAST(source_expression AS target_type DEFAULT default_expression ON ERROR)
> >
> > if so, what's the restriction of default_expression?
>
>
> The actual syntax is:
>
>
> <cast specification> ::=
>      CAST <left paren>
>          <cast operand> AS <cast target>
>          [ FORMAT <cast template> ]
>          [ <cast error behavior> ON CONVERSION ERROR ]
>          <right paren>
>
> "CONVERSION" is probably a noise word, but it is there because A) Oracle
> wanted it there, and B) it makes sense because if the <cast error
> behavior> fails, that is still a failure of the entire CAST.
>
>
> The <cast error behavior> is:
>
>
> <cast error behavior> ::=
>      ERROR
>    | NULL
>    | DEFAULT <value expression>
>
>

hi.

just want to confirm my understanding of ``[ FORMAT <cast template> ]``.

SELECT CAST('2022-13-32' AS DATE FORMAT 'YYYY-MM-DD' DEFAULT NULL ON
CONVERSION ERROR);
will return NULL.
because  ``SELECT to_date('2022-13-32', 'YYYY-MM-DD');``
will error out, so the above query will fall back to the DEFAULT
expression evaluation.