So, imho, what you can do is to prevent the system to delete a project when there are only two in a department, or to insert a new one when there are 8 projects already there.
On Tue, 2004-10-26 at 16:18, Mike Mascari wrote:
Valentin Militaru wrote: > You can do that. But first you have to do some optimisations, like: > add a column id(bigserial) to the departamens table, after which you > will replace the column department with id_department in the projects > table. It is an optimisation, as you are dealing with integer, not text. Well, that's an argument for surrogate keys, which will invoke a philosophical war amongst purists that I won't touch... > After that, what do you want to achieve? When you are inserting a > department, should the server insert 2 to 8 blank records in the > projects table which contain the inserted department? Or do you want not > to be able to insert a department if there aren't already 2 to 8 > projects containing that department in the projects table? I want the database to enforce logical consistency by ensuring that if a department exists, there are at a minimum two projects and a maximum of eight projects associated with it. Date & Darwen attribute the enforcement of such business requirements to database constraints. PostgreSQL lacks database constraints, but the result can often be achieved through triggers. But I can't figure out how to enforce consistency without deferrable triggers and without relying on the application to maintain consistency, which is not its job. Mike Mascari
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