Re: Unexpected modification of check constraint definition

Yes, using "varchar" is definitely part of why it is so odd.
There is no equality operator for "varchar", so you need an (implicit) cast to "text".

That implicit cast is made explicit when the parsed binary form of the constraint expression is
reverse engineered to a string during "pg_dump".

I'd say that the change you mention "just happened", but you can never rely on these expressions
being rendered in a fixed way - this can change any time.

But perhaps it is good enoulh if you define the constraint by casting to "text"
early: CHECK (val::text IN ('a','b','c'))

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Got it, I won't forward your mail... err...