Hello Isaac,
This is not the only area where empty tuples are not supported. Consider: PRIMARY KEY () This should mean the table may only contain a single row, but is not supported.
Yep. This is exactly the kind of case about which I was trying the command, after reading Bruce Momjian blog (https://momjian.us/main/blogs/pgblog/2020.html#June_22_2020) about one-row tables and thinking about how to improve it and allow enforcing a singleton simply, which is a thing I needed several times in the past.
On the plus side, empty rows are supported, although the explicit ROW keyword is required.
Yet another weirdness. Thanks for the comments. -- Fabien.
