Hello,
I would have designed as ship > cabin (PK of ship_id, Cabin_id)
And a separate chain of cabin_type > cabin_category > cabin
Type, and category are group classifiers and shouldn't be used to define the uniqueness of a cabin.
Take an example where the cabin category and type are defined globally for the entire fleet. Currently you'll have to
duplicatethe type, category defintions for each ship.
Doug
-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of Louis-David Mitterrand
Sent: Wednesday, March 03, 2010 9:02 AM
To: pgsql-sql@postgresql.org
Subject: [SQL] check constraint on multiple tables?
Hi,
I've got this chain of tables:
ship --> (id_ship) --> cabin_type --> (id_cabin_type) --> cabin_category--> (id_cabin_category) --> cabin
The 'cabin' table has (cabin_number, id_cabin_category ref. cabin_category)
How can I guarantee unicity of cabin_number per ship?
For now I added a unique(cabin_number,id_cabin_category) but this does
not guarantee unicity for (cabin_number,ship.id_ship).
What is the best solution? Adding an id_ship to 'cabin'? Or check'ing
with a join down to 'ship'? (if possible).
Thanks,
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