Re: SET NULL / SET NOT NULL

The SQL spec will not help us here, since it doesn't define such a
capability AFAICT.  We might do worse than to look at Or*cle's
implementation, which appears to involve a MODIFY keyword.

I find this in the Or*cle 8i documentation examples:
The following statement alters the EMP table and defines andenables a NOT NULL constraint on the SAL column:
ALTER TABLE emp    MODIFY (sal  NUMBER  CONSTRAINT nn_sal NOT NULL); 

The docs are opaque enough that I can't actually figure out a BNF
definition for ALTER TABLE MODIFY, and I don't have a working
installation to experiment against.  Can any Or*cle users here
enlighten us?
        regards, tom lane