Hi, On Tue, Apr 12, 2011 at 9:38 PM, Srdjan <srdjan@catalyst.net.nz> wrote:
1. issues table has nullable borrowernumber and itemnumber; foreign key constraints are consequently declared as "ON DELETE SET NULL ON UPDATE SET NULL"
2. That is not an isolated issue, there are many cases where foreign key field/constraints are declared like that
Can anyone shed more light, that looksvery wrong to me.
And it is very wrong; this should be tightened up. As to why? Reasons best hidden in the mists of time, no doubt. In the case of issues, I think it's pretty clear that both itemnumber and borrowernumber should be non-NULL and have foreign key constraints. I suggest ON DELETE RESTRICT ON UPDATE CASCADE; if you are deleting an item record or a patron, the application logic needs to do the right thing if for whatever reason a library really wants to delete a record that has an outstanding loan on it. Regards, Galen -- Galen Charlton gmcharlt@gmail.com