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 duplicate the type, category defintions for each ship. Doug -----Original Message----- From: pgsql-sql-ow...@postgresql.org [mailto:pgsql-sql-ow...@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, -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
