Hi,
> 2) Is there any particular reason functions like that aren't built
> into Postgres? They seem like they would be useful. (Or maybe I
> missed them?)
LEAST() and GREATEST() expressions do the same thing as yours smallest()
and largest(). See
https://www.postgresql.org/docs/current/functions-conditional.html
That might also answer the first question - just drop smallest() and
largest() and you will get two functions instead of four :-)
Now to be a little more serious, if you want a single function to both
support variadic number of arguments AND all of them in a single array,
how could the function decide whether smallest(ARRAY[1,2,3]) shall
return 1 or ARRAY[1,2,3] (which is the smallest out of all arguments)?
I would suggest not to declare such overloaded function even if it was
possible, as it might confuse the reader easily. Instead, I would go for
SELECT min(u) FROM unnest(ARRAY[1,2,3]) u
or just define a separate least_array() / greatest_array() variant.
Regards,
Ondřej Bouda