>Take for example, I have a pkey (primary key for customer) and the pkey is a unique key for installment)
>
>Do I have to put the default value for the pkey in installment as the pkey in customer?

No....assuming that customer is the parent and installment is the child, installment inherits the value of that field. You might with to change the field name in installment to avoid confusion (call it customer_fk for foreign key). Within the Insert trigger, REPLACE installment.customer_fk WITH customer.pkey