On Wed, 13 Oct 2010 12:55:40 +0200, TP <[email protected]> wrote:
> Is this legal to have a foreign key > that references several tables? It is legal, but it is uncommon or even very rare. Why? Well, a foreign key column (id_toto2_and_toto3) identifies a row (tuple) in the referred table (toto2) typically by it's primary key (id_toto2) or some other unique column (a candidate key). If that same column (id_toto2_and_toto3) also is a foreign key to another table (toto3), it identifies a row in the same way in that second table _with_ the _same_ identity. That is to say, any value in id_toto2_and_toto3 has a corresponding row in both toto2 and toto3. You have to ask yourself if toto2 and toto3 shouldn't be combined into one table. As far as I can tell, the only reason to not combine them would be some performance optimization. One should only do that to solve real performance problems, not in the initial design. -- ( Kees Nuyt ) c[_] _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
