From: Tom Lane <tgl@sss.pgh.pa.us>
To: Corey Huinker <corey.huinker@gmail.com>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions
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Comments: In-reply-to Corey Huinker <corey.huinker@gmail.com>
	message dated "Mon, 19 Dec 2022 17:56:37 -0500"
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Date: Mon, 02 Jan 2023 10:57:27 -0500
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Corey Huinker <corey.huinker@gmail.com> writes:
> The proposed changes are as follows:
> CAST(expr AS typename)
>     continues to behave as before.
> CAST(expr AS typename ERROR ON ERROR)
>     has the identical behavior as the unadorned CAST() above.
> CAST(expr AS typename NULL ON ERROR)
>     will use error-safe functions to do the cast of expr, and will return
> NULL if the cast fails.
> CAST(expr AS typename DEFAULT expr2 ON ERROR)
>     will use error-safe functions to do the cast of expr, and will return
> expr2 if the cast fails.

While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.
If we know that they are about to standardize exactly this syntax,
where is that information available?  If we don't know that,
I'd prefer to invent some kind of function or other instead of
extending the grammar.

			regards, tom lane