函式lnnvl

今天看執行計劃,無意中發現過濾的時候使用一個不知道的函式lnnvl,google發現如下連結,記錄如下:

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