I have a reference which is guaranteed not to have a valid reference
(preferably NULL) until it is processed later. How can I defer a
reference entry so that both NULL and an actual reference are valid in
the reference field? The processing which I speak of takes place later
and not in the same transaction (thus making DEFERRABLE useless,
right?). A solution I thought of is to forget keys and just make it an
INT8 since I am also guaranteed that its referenced item is never
deleted. But certainly, there is a more reliable way to do it, right?
In summary, what I want is

field INT8 REFERENCES sometable NULL OK

or

field INT8 CHECK(SELECT id FROM someothertable WHERE field=id)

(can I do this? this allows NULL right?)

The rule is ref2 can either be a valid reference or NULL.
CREATE TABLE thetable(
ref2 INT8 REFERENCES someothertable,
...
);

Thanks for any help.
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AgentM
agentm(at)cmu(dot)edu