Alan McDonald wrote:

> I notice that SYSTEM TABLES generally don't have PKs, nor unique
> constraints, merely unique indices.
>
> ...is there history in this? e.g.
> the concept PKs didn't exist when the engine started dev.

The concept existed, but not in GDML - the native language of
the system tables.

> Or is performance better without these constraints and the engine "protects
> itself" in their absence?
>

There's no performance penalty for primary keys and the performance
impact of foreign keys is less than the cost of the check that is
now done explicitly.

Regards,


Ann