to update using cascade

I created customer table with cust_id as primary key...and
then created a department table and used cust_id as its foreign key...
I tried updating the cust_id in the customer table bt got an error 'violations..child found'.
how to update cust_id in both the tables using CASCADE?

@ aarthi,

How did u check whether cust_id is set as foreign key in department table ?

I am not able to enter value for cust_id for department table that is not in customer table.
it says integrity constraint violated parent-key not found!!!

I think
using cascade you can delete all the record in dept table if the related row in cust table id deleted.. As for Update, You can update all the data except the related column(custid).
No point in using cascade to update the foriegn key by itself.