For the time being, I just changed the bitwise NOT to :~~ and added
the :~ to the def-infix-ops forms. Is this something you overlooked
or is there another way to access regular expressions functionality?

Good question. I never really use the regexp functionality, so I didn't really think about this. It looks like regular expression matching always takes two arguments, while bitwise NOT only takes one, so I think a good solution would be to make that operator behave like minus and allow both binary infix and unary prefix application. I'll add the other regexp operators (~*, !~, and !~*) too, while I'm at it.

Third, since I see you care about the documentation, I think you
should point out in the documentation that the deftable form must
define the table columns in the same order with its PostgreSQL
counterpart, since you use the * abbreviation in the get-dao select
statement. Otherwise, the get-dao does not work.

You have a point there. I assumed people would create their tables from the lisp definition, in which case everything works fine. This will probably also be an issue when you end up adding or dropping rows in tables -- the best solution is probably to fix dao-loading so that it takes column names into account. This might make it a bit slower, but right now it's just confusing. I'll try to fix this this week.

Finally, is there a way to access the constraints of an SQL table from
the Lisp side? I have not managed to find anything related yet.

No, though this is something that I definitely want to add. Unfortunately I'm a bit tied up with other work at the moment, so it might take a while. If you feel up to it, a patch would be welcome.