> Based on past discussions I've done a prototype implementation

allowing

> domains and NOT NULL to be used in PSQL.
> See that as another call for discussion on the topic.

Oracle also permit to specify a table.column as datatype.
Syntax is somewhat clunsky:

declare
my_variable myschema.mytable.mycolumn%TYPE;

The advantage here is to have the same type as the field you're using.
Although there are a dependency between the table and the procedure,
changing one, will directly invalidate other.

Maybe the change should restrict for column and don't for domains in
initial implementation:

declare my_var type of column table.column;