select {fn length("hello")}, { date "1997-10-20" };
{fn length("hello")}	1997-10-20
5	1997-10-20
create table t1 (a int not null auto_increment,b int not null,primary key (a,b));
insert into t1 SET A=NULL,B=1;
insert into t1 SET a=null,b=2;
select * from t1 where a is null and b=2;
a	b
2	2
select * from t1 where a is null;
a	b
explain select * from t1 where b is null;
Comment
Impossible WHERE noticed after reading const tables
drop table t1;