Re: ERROR: failed to find conversion function from unknown to text

On Thu, Jan 29, 2026 at 9:24 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Is there a good reason why that shouldn't be an error?

at that time, i want
select cast('a'::text as unknown);

behave the same as

select cast('a' as unknown);

To make it an error, meaning it's not possible to coerce to the unknown type.
We can do it in the function find_coercion_pathway, just
after the ``if (sourceTypeId == targetTypeId)`` check:

    if (targetTypeId == UNKNOWNOID)
        return COERCION_PATH_NONE;

it's also doable in the function can_coerce_type,
right after the ``if (inputTypeId == UNKNOWNOID)``:

        if (targetTypeId == UNKNOWNOID)
            return false;



--
jian
https://www.enterprisedb.com/