1
1
create table t1 (a int, b int not null, c int null, d int not null, pk int primary key);
3
3
insert into t1 values (0,0, 0, 0,0);
5
5
insert into t1 values (NULL, NULL, NULL, NULL, 1);
6
6
insert into t1 values (NULL, 1, NULL, 1, 2);
8
8
insert into t1 values (1,2,3,NULL, 3);