What are the Pros and Cons of Cascading delete and updates?

Question

Maybe this is sort of a naive question...but I think that we should always have cascading deletes and updates. But I wanted to know are there problems with it and when should we should not do it? I really can't think of a case right now where you would not want to do an cascade delete but I am sure there is one...but what about updates should they be done always?

So can anyone please list out the pros and cons of cascading deletes and updates ? Thanks.

Answer 1

Pros:

• When you delete a row from the Parent table all the foreign key rows are deleted
• This is usually faster than implementing this with triggers
• Orphaned rows are unlikely

Cons

• Orphans are possible
• If by mistake you delete a row in the parent table all the rows in the corresponding child tables will be deleted and it will be PITA to figure out what you deleted

Answer 2

This depends on the entities that are contained in the tables: if the side of the foreign key cannot exist without the side of the primary key, it makes sense to have cascaded delete.

E. g.: An invoice line item does not have any right to survive if the invoice is deleted.

But if you have a foreign key used for the relationship "works for" for the relationship between an employee and his/her boss, would you want to delete the employee if the boss leaves the company?

In addition: a technical issue is that some ORM (object relational mapping) tools are confused if dependent table entries change without them being responsible for that.

Answer 3

Pros:

• Data integrity - Can help avoid situations where a record refers to something that is no longer there.

Cons:

• Performance - Cascading deletes/updates can be sloooooooooooooooooooow.
• Complexity - It seems most people I work with are not used to cascades, so when you give them a new project that has it, they're a bit surprised the first time they trigger one of these cascades.
• As others have already mentioned, can really mess things up when used improperly.

Answer 4

Pro: it allows you to reduce the quantity of SQL statements needed to perform delete actions.

Con: you could delete data that somewhat may be important for auditing in a later time. So it's important to keep it even if the parent row has been deleted. In this case the foreign key should receive a NULL value for example.