Sean Chittenden <sean(at)chittenden(dot)org> writes:
> Does the optimizer optimize away the foreign key checks on a primary
> key if its value doesn't change, even though it's had a value assigned
> to it?
The optimizer has nothing to do with this, but in most cases the foreign
key triggers themselves will short-circuit when the key value is found
to be the same as before.
regards, tom lane