Re: SQL for Modeling Generalization Hierarchies

--CELKO-- (jcelko212_at_earthlink.net) writes:
> CREATE TABLE Vehicles
> (vin CHAR(17) NOT NULL PRIMARY KEY,
> vehicle_type CHAR(3) NOT NULL
> CHECK(vehicle_type IN ('SUV', 'SED')),
> UNIQUE (vin, vehicle_type),
> ..);
>
> Notice the overlapping candidate keys. I then use a compound candidate
> key (vin, vehicle_type) and a constraint in each sub-class table to
> assure that the vehicle_type is locked and agrees with the Vehicles
> table. Add some DRI actions and you are done:

Ah! Interesting trick! I'll save a mental note about that.

-- 
Erland Sommarskog, SQL Server MVP, sommar_at_algonet.se

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