Deleting hierarchical data in SQL table

Question

I have a table with hierarchical data.
A column \"ParentId\" that holds the Id (\"ID\" - key column) of it\'s parent.

When deleting a row, I want to delete all c

Answer 1

Depends on your database. If you are using Oracle, you could do something like this:

DELETE FROM Table WHERE ID IN (
  SELECT ID FROM Table
  START WITH ID = id_to_delete
  CONNECT BY PRIOR.ID = ParentID
)

ETA:

Without CONNECT BY, it gets a bit trickier. As others have suggested, a trigger or cascading delete constraint would probably be easiest.

Answer 2

Add a foreign key constraint. The following example works for MySQL (syntax reference):

ALTER TABLE yourTable
ADD CONSTRAINT makeUpAConstraintName
FOREIGN KEY (ParentID) REFERENCES yourTable (ID)
ON DELETE CASCADE;

This will operate on the database level, the dbms will ensure that once a row is deleted, all referencing rows will be deleted, too.