On Mon, Jul 6, 2026 at 11:56 PM Haibo Yan <[email protected]> wrote: > I now think my v2 patch is too broad. It tries to make CAST(... FORMAT ...) > a generic user-defined format-cast mechanism, but SQL feature T839 is much > narrower: formatted casts between datetime types and character strings. > > So I think the next version should move back closer to Jian’s original scope: > support T839 first, rather than introduce pg_format_cast and > CREATE FORMAT CAST. I still think we should avoid ad-hoc parser rewrites to > specific function names, but the feature scope should be the standard > datetime/string cases, not arbitrary source/target pairs. > > I also think it would be useful to retitle this thread around the standard > feature, for example: > > Support SQL feature T839: formatted casts between datetime and > character strings > > That seems to describe the real target better than a generic format-cast > facility.
My current point of view is that your patch does exactly the right thing but it's not clear whether we want it. I mean, if we eventually want to support this feature with arbitrary types, there is no reason not to do so from the start. Or at least, none that I can see. But that does not address the question of whether we want the feature in the first place, which is debatable. -- Robert Haas EDB: http://www.enterprisedb.com
