Foreign key mapped to a unique constraint

Question

ok here is the issue
create table parent(col1 char, col2 char);
alter table parent add constraint pk_parent primary key(col1);
alter table parent add constraint uk_parent unique(col1,col2);
insert into parent values('A','7');
*1 row created.*
create table child(col1 char, col2 char);
alter table child add constraint fk_child_parent foreign key(col1,col2) references parent(col1,col2);
insert into child values('B','4');
insert into child values('B','4')
ERROR at line 1:
ORA-02291: integrity constraint (WILDGOD.FK_CHILD_PARENT) violated - parent key
not found
thats what i expect....but
insert into child values('B',NULL);
*1 row created.*
why does it let me do this, i realize its because col2 is NULL but shouldnt it still check for col1 to be in the parent?
Please clarify, thanks in advance.

Answer 1

I see the same & am not sure why either.
SQL> @a
SQL> create table parent(col1 char, col2 char);
Table created.
SQL> alter table parent add constraint pk_parent primary key(col1);
Table altered.
SQL> alter table parent add constraint uk_parent unique(col1,col2);
Table altered.
SQL>
SQL> insert into parent values('A','7');
1 row created.
SQL> create table child(col1 char, col2 char);
Table created.
SQL> alter table child add constraint fk_child_parent foreign key(col1,col2) references parent(col1,col2);
Table altered.
SQL>
SQL> insert into child values('B','4');
insert into child values('B','4')
ERROR at line 1:
ORA-02291: integrity constraint (DBADMIN.FK_CHILD_PARENT) violated - parent key not found
SQL>
SQL> insert into child values('B',NULL);
1 row created.
SQL>
SQL> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE     11.2.0.1.0     Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production