Add Add ON DELETE CASCADE To Foreign Key Constraint as a postgres til

postgres/add-on-delete-cascade-to-foreign-key-constraint.md

@@ -0,0 +1,30 @@
+# Add ON DELETE CASCADE To Foreign Key Constraint
+
+The `alter table` command lets you do quite a bit. But when it comes to
+altering existing constraints, there is not much you can do. If you want to
+add an `on delete cascade` to an existing foreign key constraint, you are
+going to need two statements.
+
+The first statement will drop the constraint and the second statement will
+recreate it with the addition of the `on delete` clause. Furthermore, you'll
+want to do this in a transaction to ensure the integrity of your data during
+the transition between indexes.
+
+Here is an example:
+
+```sql
+begin;
+
+alter table
+drop constraint orders_customer_id_fkey;
+
+alter table
+add constraint orders_customer_id_fkey
+foreign key (customer_id)
+references customers (id)
+on delete cascade;
+
+commit;
+```
+
+[source](http://stackoverflow.com/questions/10356484/how-to-add-on-delete-cascade-constraints)