SharePoint 2010: Enforce Primary Key and Referential integrity in List
After enabling the Enforce unique values, entering the duplicate value will throw the error message as follows
If you are using any Lookup column in a List we have the option to enable referential integrity on that column.
In SharePoint 2010, there are two types of option
Restrict Delete: Deleting a parent item which has a reference in the child item will not allowed and will through the error.
Cascade Delete: Deleting the parent item will delete the corresponding Child item(s).
If Cascade Delete is enabled for the lookup column following warning message will be shown on deleting the parent Item.
On Clicking Ok it will Delete the corresponding child items too.
If you check the recycle bin after deletion, you will be shown like this.
In Recycle bin only the parent item will be shown. But the Icon (type) which will represent that it holds some child items. [Icon looks something like relationship in tables].
On restoring this item will also restore the corresponding child items.