Comments on: on delete cascade http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html Oracle Certified Master Mon, 01 Dec 2008 17:44:38 +0000 http://wordpress.org/?v=2.6.5 By: Omar_emp http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-8212 Omar_emp Tue, 28 Oct 2008 16:32:18 +0000 http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-8212 it s a very clear exemple ! Thanks i m a lot less stupid now ! Regards it s a very clear exemple !

Thanks i m a lot less stupid now !

Regards

]]> By: Salese http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-5031 Salese Wed, 17 Oct 2007 15:56:17 +0000 http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-5031 Great examples! I'm just start learning Oracle and you helped me a lot. Regards. Great examples! I’m just start learning Oracle and you helped me a lot.
Regards.

]]> By: joel garry http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4680 joel garry Fri, 07 Sep 2007 17:57:06 +0000 http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4680 No, I'll just post about it on <a href="http://groups.google.com/group/comp.databases.oracle.misc/msg/93f3829a36e2c3de?dmode=source" rel="nofollow">usenet</a>. :-) No, I’ll just post about it on usenet. :-)

]]> By: Laurent Schneider http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4620 Laurent Schneider Thu, 30 Aug 2007 19:22:14 +0000 http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4620 Thanks John, I expected that comment! Triggers can be very useful, that is sure. I just wanted to show that they can be evil when they produce unexpected results. About orders, it is a good example. This features could be used, but should not be misused 8-) Thanks John, I expected that comment! Triggers can be very useful, that is sure. I just wanted to show that they can be evil when they produce unexpected results. About orders, it is a good example.

This features could be used, but should not be misused 8-)

]]> By: John Flack http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4618 John Flack Thu, 30 Aug 2007 12:22:45 +0000 http://laurentschneider.com/wordpress/2007/08/on-delete-cascade.html#comment-4618 Yes, both referential integrity constraints and triggers can have unexpected, and unreported effects. Does that mean we shouldn't use them? No! It means that we should use them with extreme care, and planning and good design. We should also document them thoroughly. For instance, do we really want a cascade delete on the FK between departments and employees? No, if we had done our analysis right, we would know that an employee is an independent entity from a department and does not disappear just because the department does. We might want to null the FK on EMP, but if we do, we need a cleanup process to prompt a human to assign the employees to other departments. However, let's consider Orders and Order Line Items. Line Items are not necessarily independent of the Orders on which they appear. So we may very well want to cascade the delete from Orders to Order Line Items. The fact that Oracle only reports one Order deleted is fine - the line items are part of the one order. Yes, both referential integrity constraints and triggers can have unexpected, and unreported effects. Does that mean we shouldn’t use them? No! It means that we should use them with extreme care, and planning and good design. We should also document them thoroughly. For instance, do we really want a cascade delete on the FK between departments and employees? No, if we had done our analysis right, we would know that an employee is an independent entity from a department and does not disappear just because the department does. We might want to null the FK on EMP, but if we do, we need a cleanup process to prompt a human to assign the employees to other departments. However, let’s consider Orders and Order Line Items. Line Items are not necessarily independent of the Orders on which they appear. So we may very well want to cascade the delete from Orders to Order Line Items. The fact that Oracle only reports one Order deleted is fine - the line items are part of the one order.

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