Re: Implementing standard SQL's DOMAIN constraint

On Wednesday, January 2, 2019, Rich Shepard <rshepard(at)appl-ecosys(dot)com>
wrote:

> On Wed, 2 Jan 2019, David G. Johnston wrote:
>
> There is no magic name logic involved. A domain is just a type with
>> inherent constraints that are user definable. You make use of it like any
>> other type.
>>
>> Create table tbl (
>> column_name state_code not null
>> )
>>
>> Values stored in column_name are now of type state_code and constrained to
>> be one of the check constraint values.
>>
>
> David,
>
> I'm not following you. I have two tables each with a column,
> state_code char(2) NOT NULL.
>
> Do you mean that I need to write the column constraint for each table? If
> not, I don't see from your response how to implement the multi-table
> constraint for this column.
>
>
That is a char(2) column for which ‘??’ is a valid value. The fact that it
is named state_code is immaterial; the domain that you created doesn’t get
used. There is no magic linking just by virtue of using the same name.

Change char(2) to state_code if you wish to apply the domain on the column.

David J.