I agree with Arno. If you're implementing true domains, make them
behave like a domain.

If you implement a "type of" or "based on" feature, make it copy the
datatype only and invalidate whenever the datatype changes.

Martijn Tonies
Database Workbench - tool for InterBase, Firebird, MySQL, NexusDB, Oracle &
MS SQL Server
Upscene Productions
http://www.upscene.com
My thoughts:
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Database development questions? Check the forum!
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> >>> Per SQL-2003, CAST(<value> AS <domain name>) is perfectly legal, so
> >>> I agree here.
> >>>
> >> Yes, but if we have syntax that apply and that not apply constraints we
> >> need two syntax for cast too.
>
> > Why? CAST knows nothing about constraints and it shouldn't. Casting some
> > value to domain D should not mean that the value will acquire any

constraint

> > definition from D. It's about datatypes only.
>
> I'm not sure i understand your point, but the result of CAST(<value> AS

<domain>) should meet the domain constraints.

>
> This is from the SQL standard:
>
> --------------------------------------------------------------------------

------

> 4.17.4 Domain constraints
> A domain constraint is a constraint that is specified for a domain. It is

applied to all columns that are based on

>
> that domain, and to all values cast to that domain.
>
> 68 Foundation (SQL/Foundation)
>
> IWD 9075-2:200x(E)
>
> 4.17 Integrity constraints
>
> A domain constraint is described by a domain constraint descriptor. In

addition to the components of every

>
> constraint descriptor, a domain constraint descriptor includes:
>
> - The template <search condition> for the generation of domain constraint

usage <search condition>s.

>
> - A possibly empty set of domain constraint usages.
>
> A domain constraint usage descriptor is created implicitly by the

evaluation of a <column definition> whose

>
> <data type or domain name> is a <domain name>. If C is such a column and D

is the domain identified by the

>
> <domain name>, then every domain constraint DC defined for D implies a

domain constraint usage, to the

>
> effect that each value in C satisfies DC.
>
> In addition to the components of every table constraint descriptor, a

domain constraint usage descriptor includes:

>
> - The name of the applicable column.
>
> - The applicable <search condition> that evaluates whether each value in C

satisfies DC.

>
> A domain constraint is satisfied by SQL-data if and only if, for every

table T that has a column named C based

>
> on that domain, the applicable <search condition> recorded in the

appropriate domain constraint usage evaluates

>
> to True or Unknown.
>
> A domain constraint is satisfied by the result of a <cast specification>

if and only if the specified template

>
> <search condition>, with each occurrence of the <general value

specification> VALUE replaced by that result,

>
> evaluates to True or Unknown.
> --------------------------------------------------------------------------

------

>
> > 1) Any domain change marks all dependent BLRs as invalid. Any parsing or
> > execution of such BLR is rejected with an appropriate error. This

"invalid"

> > flag is cleared as soon as the BLR gets successfully regenerated and

parsed.

> > The flag is persistent, so it should be stored in the schema. This is

the

> > most reliable approach, as it should catch all possible errors, but it's
> > also quite hard in use (it requires manual processing and perhaps also

SQL

> > source to be available).
>
> Why SQL-source? To give a good report to user?
>
> Regards,
> Arno Brinkman
> ABVisie
>
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