Question

Does DB2 version 8 z/OS support nullable foreign keys?

For example, a foreign key on a person table to the supervisor table (where some people do not have supervisors).

Answer 1

According to the documentation, it should be possible to have a foreign key that is nullable in DB2 for z/OS v8. See the insert, update, and delete rules for these details:

insert rule
A nonnull insert value of the foreign key must match some value of the parent key of the parent table. The value of a composite foreign key is null if any component of the value is null.

update rule
A nonnull update value of the foreign key must match some value of the parent key of the parent table. The value of a composite foreign key is treated as null if any component of the value is null.

delete rule
Controls what happens when a row of the parent table is deleted. The choices of action, made when the referential constraint is defined, are RESTRICT, NO ACTION, CASCADE, or SET NULL. SET NULL can be specified only if some column of the foreign key allows null values.

Site reference: http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=%2Fcom.ibm.db2.doc.sqlref%2Frcncrfi.htm

DB2 v8 Foreign Key Clause reference (also notes that nulls are allowed): http://publib.boulder.ibm.com/infocenter/db2luw/v8/index.jsp?topic=/com.ibm.db2.udb.doc/admin/c0004981.htm