db :: adding "missing" foreign key constraints (tsql)

I had the following tables

create table customer (
 id int identity primary key,
create table foo_orders (
 orderno int identity primary key,
 customerid int,

after various failed attempts at “alter column”, “add constraint”, etc. I finally found the correct incantation

alter table foo_orders with nocheck add foreign key(customerid)
references customer(id)
on delete no action
on update no action

In (other) words:

  • in the foo_orders table
  • create a new foreign key
    • from the customerid field
    • to the id field in the customer table
  • don’t check existing data in the table (with nocheck)
  • if the customer is deleted, keep the foo_orders record (on delete no action)
  • if the id field in the customer table changes, then do nothing (on update no action)

(at least that’s what I’m pretty sure it means 😉

Why the no action clauses? The foo_order table records info we send to external entities, and is part of the historical record.  Any changes should never happen automagically.

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