Louis, Interesting discussion. Always fun to think about real world stuff.
We have a similar problem for comparing hotel rooms. So the issue is that you aren't originating the data, just classifying it. I'd move toward a scheme where you reclassify the line marketing speak to common lay terms. You're trying to help consumers compare. Exactly what the marketers don't want them to do. After all a silk purse is just a sow's ear without marketing. :) 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 10:18 AM To: pgsql-sql@postgresql.org Subject: Re: [SQL] check constraint on multiple tables? On Wed, Mar 03, 2010 at 04:05:43PM -0000, Oliveiros wrote: > > As your table names seem to imply, type and category are cabin's > characteristics , not ship characteristics. > Am I right? Yes and no :) - I'm scanning cruise line web sites with a spider to collect prices so I'm building cabin_type's and cabin_category's on the fly, - each ship class (a cruise line has several) has its own particular types (Celebrity Xpedition is the only one with "Xpedition suite" type, etc.) > As Richard pointed out, maybe you could add a relationship between > cabin and ship and drop the relationship between ship and > cabin_category you now have > Then you could add that uniqueness restriction. That's one option. > Also, the relationship between type and category is one to many ? Or > can it be many to many? Put other way, is this overlap between the > categories that belong to different "types" ? One cabin_type to many cabin_category's, for example: - "Sunset Veranda Stateroom" (type) can be on "Vista", "Panorama", etc. decks (category) with a different price, But it's true that there is some overlap in categories between different ships. > If the later applies, maybe > you could have cabin refer to both type and category tables and drop > the relation between type and category. > > The cabin table would then work as an associative table between > category and type. > > Ain't saying your schema is wrong, maybe you have strong reasons to > do that that way, that I am not realizin by now... You got me thinking about it. Thank you for your interesting comments. -- 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
