Re: BUG #18594: CASE WHEN ELSE failing to return the expected output when the same colum is used in WHEN and ELSE

On Tue, 18 Feb 2025 at 10:12, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Yeah. We document somewhere that the contents of a literal string are
> *not* considered while deciding what type it should be taken as; thus,
> the possibility of a casting failure is not part of the rules.
>

The length of a literal is not strictly speaking its "contents". One could
for example, have its type as varchar(x) where x is its length. And then
not have implicit typecasts from varchar(x) to varchar( < x).

> I think such a rule would be pretty dangerous, even if we could
> implement it easily. As an example, if you entered something you
> meant as a timestamp, but you fat-fingered the punctuation or
> something, it'd likely fall back to being considered just "text",
>

I don't get that, I thought timestamps have to be preceded by "TIMESTAMP".

potentially silently changing the semantics of the expression. We had

> a lot of trouble with that sort of behavior back when the system had a
> lot of implicit casts to text. We got rid of (most of) those in 8.3
> or thereabouts, and it made the semantics generally a lot safer.

So... you solved that, it sounds like.

And yet this super dangerous behavior which could sit dormant and
undiscovered in a view in a large computer system, doesn't bother anyone?
OK, whatever.

Chris