Hi ng,
(Oracle 9.2.0.7i)
I talk about a database concerning real Trees.
There is a table TTrees.
A single Tree belongs either to a forrest or to a street or to a park or
whatelse.
So there exist f.e. a table TStreets and a table TForrests.
in the table TTrees actually exist a field for each Table, f.e.
CIDFORREST
CIDSTREET
Exactly 1 of them is not NULL, all the others are definitely NULL.
Now my Questions:
Is there a way to substitute this by only 1 Field, f.e. CID_BELONGS_TO
_AND_ to build a FK-constraint like
TForrests.CID=TTrees.CID_BELONGS_TO OR
TStreets.CID=TTrees.CID_BELONGS_TO ...
?
Is there a possibility to build a constraint, that observes that _exact_
1 of the fields (CIDFORREST, CIDSTREET ..) is not null? (I know, I could
use triggers for it)?
Is there a better way to build this database? (The Columns of TTrees are
95% equal, no matter if it stands on a street or in a forrest, so there
is only 1 table)
Many thanks
Andreas Mosmann
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