Re: cast to domain with default collation issue.

On Tue, May 24, 2022 at 7:42 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> I wrote:
> > Perhaps this should be documented more clearly, but it's not obviously
> > wrong.  If the domain declaration doesn't include an explicit COLLATE
> > then casting to the domain doesn't create an explicit collation
> > requirement.  (That is, the domain *doesn't* have a specific
> > collation attached to it, any more than type text does.)
>
> Perhaps we could improve matters like this?
>
> diff --git a/doc/src/sgml/ref/create_domain.sgml
> b/doc/src/sgml/ref/create_domain.sgml
> index 81a8924926..e4b856d630 100644
> --- a/doc/src/sgml/ref/create_domain.sgml
> +++ b/doc/src/sgml/ref/create_domain.sgml
> @@ -94,7 +94,8 @@ CREATE DOMAIN <replaceable
> class="parameter">name</replaceable> [ AS ] <replacea
>        <listitem>
>         <para>
>          An optional collation for the domain.  If no collation is
> -        specified, the underlying data type's default collation is used.
> +        specified, the domain has the same collation behavior as its
> +        underlying data type.
>          The underlying type must be collatable if
> <literal>COLLATE</literal>
>          is specified.
>         </para>
>
>
+1

The lack of any explicitness pushes evaluation down to the base type -
which is a behavioral thing as opposed to some kind of attribute it
possesses.

David J.