1 create table t1(f1 int,f2 int,f3 int);
2 insert into t1 values(1, 10, 100);
3 insert into t1 values(2, 20, 200);
4 insert into t1 values(3, 30, 300);
5 insert into t1 values(NULL, 20, 500);
6 insert into t1 values(12, 20, 500);
7 insert into t1 values(1, NULL, 400);
8 insert into t1 values(1, 11, 500);
9 insert into t1 values(13, 30, 200);
10 insert into t1 values(14, 31, 300);