Question

In Oracle I have a table called Category consisting of three columns:
ID = which is system produced unique key ,
Catgeory_name = which is 300 char ,
and parent_id = which either could be -1 which means no parent for this category, or it could be a value from the ID column described earlier as the parent_id.

The problem is when I delete a category who is a parent, I need to automatically delete all the children as well. My question is : Does SQL provide any means to do this automatically or should I take care of it in my upper layer langugae which is C#.

For example if there was a foreign key situation between two tables, I know SQL provides ON DELETE CASCADE to delete the dependent records as well as the parent record upon a delete request for the origianal record.

However, I don’t know of any way in SQL that would take care of the above situation automatically, meaning when the parent is deleted in the above table, all the children get deleted as well.

Thanks in advance for your help.

Answer 1

If the parent_id was set to NULL if there was no parent, you could define a foreign key on category that referenced the primary key in category

SQL> create table category (
  2    id number primary key,
  3    category_name varchar2(300),
  4    parent_id number references category( id )
  5  );

Table created.

You could then declare that foreign key constraint to automatically delete the children when the parent row is deleted.

If you really want to use a magic value of -1 to indicate the absence of a parent rather than using a proper NULL, you could potentially insert a row into the category table with an id of -1 and then create the foreign key constraint. But that is much less elegant than using a NULL.