drop table if exists t1;
CREATE TABLE t1
(
pk1 INT primary key,
key1 INT,
key2 VARCHAR(20),
key3 VARCHAR(20)
);
insert into t1 values(1,12,'a','a1'),(2,11,'a','b1'),(3,10,'b','b1'),(4,9,'c','c1'),
(5,8,NULL,'d1'),(6,7,NULL,'b1'),(7,6,NULL,'b1'),
(8,5,'a',NULL),(9,4,'a',NULL),(10,3,NULL,NULL),
(11,2,'',NULL),(12,1,NULL,'');
create index i1 on t1(key2,key3);
select * from t1 where key2='a' and key3=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2='a' and key3=NULL;
pk1
select * from t1 where key2='a' and key3>NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2='a' and key3>NULL;
pk1
select * from t1 where key2='a' and key3<NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2='a' and key3<NULL;
pk1
select * from t1 where key2='a' and key3>=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2='a' and key3>=NULL;
pk1
select * from t1 where key2='a' and key3<=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2='a' and key3<=NULL;
pk1
select * from t1 where key2=NULL and key3='b1';
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3='b1';
pk1
select * from t1 where key2>NULL and key3='b1';
pk1	key1	key2	key3
select pk1 from t1 where key2>NULL and key3='b1';
pk1
select * from t1 where key2<NULL and key3='b1';
pk1	key1	key2	key3
select pk1 from t1 where key2<NULL and key3='b1';
pk1
select * from t1 where key2>=NULL and key3='b1';
pk1	key1	key2	key3
select pk1 from t1 where key2>=NULL and key3='b1';
pk1
select * from t1 where key2<=NULL and key3='b1';
pk1	key1	key2	key3
select pk1 from t1 where key2<=NULL and key3='b1';
pk1
select * from t1 where key2=NULL and key3=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3=NULL;
pk1
select * from t1 where key2=NULL and key3<NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3<NULL;
pk1
select * from t1 where key2=NULL and key3>NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3>NULL;
pk1
select * from t1 where key2=NULL and key3<=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3<=NULL;
pk1
select * from t1 where key2=NULL and key3>=NULL;
pk1	key1	key2	key3
select pk1 from t1 where key2=NULL and key3>=NULL;
pk1