Re: Questions on domain on composite / casts ignoring domains

Jim Nasby-5 wrote
> I'm trying to create what amounts to a new type. This would be rather easy
> if I could perform a CHECK on a composite type, which I could do if I
> could create a domain on top of a composite. Is there any reason in
> particular that hasn't been done?
>
> As an alternative, I tried accomplishing this with a straight domain. That
> would work, except for this:
>
> WARNING: cast will be ignored because the source data type is a domain
>
> Why do we ignore casts from domains to other data types? I'm guessing
> because it's simply not what domains were meant for?

A domain is a base type with a constraint. When you cast you already know
the existing value is valid and the system simply uses the cast available
for the base type instead. i.e., You cannot have a domain with a different
cast rule than the base type over which it is defined.

Likely the lack of capability is simply a matter of complexity in the face
of somewhat uncommon usage and limited resources.

David J.

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