Re: Why does Postgres allow duplicate (FK) constraints

Tom Lane, 26.03.2013 17:16:
> The lack of any prohibition to the contrary means there is no way to
> argue that the code you showed previously violates the spec; thus,
> a database that fails to accept it is rejecting spec-compliant DDL.

I'm not claiming that the spec is violated...
(And I'm not complaining either. I'm just curious if there was a technical reason)

> Well, it's redundant, but that doesn't make it wrong.  In any case,
> there are lots of ways that things might be redundant.  Should we
> reject a unique constraint on (a,b) if there's already one on (b,a)?
> Or if there are separate unique constraints on each of a and b?

Hmm, good point.

Although I think a definition that is identical with regards of the columns and their position in the constraint
_could_be considered identical. 

Anyway thanks for the feedback.