函数lnnvl

今天看执行计划,无意中发现过滤的时候使用一个不知道的函数lnnvl,google发现如下链接,记录如下:
http://www.adp-gmbh.ch/ora/sql/lnnvl.html

create table lnnvl_ex (
a number,
b number
);

insert into lnnvl_ex values (null, null);
insert into lnnvl_ex values (null, 1);
insert into lnnvl_ex values ( 2, 2);
insert into lnnvl_ex values ( 3, null);
insert into lnnvl_ex values ( 4, 5);

select * from lnnvl_ex where a=b;

A B
---------- ----------
2 2

select * from lnnvl_ex where lnnvl(a=b);

A B
---------- ----------

1
3
4 5