Re: Not In Foreign Key Constraint

2013/9/19 David Johnston <polobo(at)yahoo(dot)com>

> Misa Simic wrote
> > I guess that rule can be achieved with triigers on TableA and TableC -
> but
> > the same is true for FK (and FK constraint is more effective then trigger
> > -
> > that is why I wonder would it be useful/achievable to create that kind of
> > constraint)
> >
> > Thoughts, ideas?
>
> You create a common "keys in use" table and only insert a record into the
> main tables if you can successfully add the desired key to the shared keys
> table ( as a unique value ). Setup a normal FK to that table to help
> enforce that valid records must exist on the keys table. Not fool-proof
> but
> you only need to worry about insertions - delete from the pk table to
> remove
> the record from the main table and free up the key.
>
> David J.
>
>
>
>
>

Thanks David,

Yes, that is one of ways that goal can be achieved via triggers (or to let
someone else worry about that Key is inserted/updated/deleted in Master
Table first...)

Constraint - should be more effective way... (It shouldnt be mixed with FK
constraint - even it is opposite on some kind... - it was just simplest way
to describe the feature)

And it should ensure that every row in table is valid from moment it is
created (what trigger can't ensure - constraint does it - or constraint
cant be created etc)

Thanks,

Misa