On delete set null

DB2 has a referential integrity rule "on delete null" for tables linked by foreign keys. This feature is now available for Oracle (version 8.i)

SQL> create table emp ( empno int primary key, 
         deptno int references dept(deptno) 
         on delete set null );

In earlier versions of Oracle, this can be implemented but requires the use of complicated triggers (the complexity being from the need to avoid mutating table errors)