SQL> create table registrations
2 ( attendee NUMBER(4)
3 , course VARCHAR2(6)
4 , begindate DATE
5 , evaluation NUMBER(1)
6 , constraint R_PK primary key(attendee,course,begindate)
7 ) ;
Table created.
SQL>
SQL> insert into registrations values (2,'SQL',date '2009-04-12',4 );
1 row created.
SQL> insert into registrations values (14,'SQL',date '2009-04-12',5 );
1 row created.
SQL> insert into registrations values (6,'SQL',date '2009-04-12',4 );
1 row created.
SQL> insert into registrations values (11,'SQL',date '2009-04-12',2 );
1 row created.
SQL> insert into registrations values (8,'SQL',date '2009-10-04',NULL);
1 row created.
SQL> insert into registrations values (9,'SQL',date '2009-10-04',3 );
1 row created.
SQL> insert into registrations values (13,'SQL',date '2009-10-04',4 );
1 row created.
SQL> insert into registrations values (13,'SQL',date '2009-12-13',NULL);
1 row created.
SQL> insert into registrations values (6,'SQL',date '2009-12-13',NULL);
1 row created.
SQL> insert into registrations values (3,'OAU',date '2009-08-10',4 );
1 row created.
SQL> insert into registrations values (12,'OAU',date '2009-08-10',4 );
1 row created.
SQL> insert into registrations values (13,'OAU',date '2009-08-10',5 );
1 row created.
SQL>
SQL> column evaluation NULL "unknown!!!"
SQL>
SQL> select * from registrations
2 where attendee = 4;
no rows selected
SQL>
SQL>
SQL> drop table registrations;
Table dropped.