Oracle nvl函数有关问题

Oracle nvl函数问题
String queryString = " from TProject where nvl(submit,'no') = 'no' ";

nvl(submit,'no')的意思是 假如submit字段值为空 那么submit=no  

那么nvl(submit,'no')='no'的意思是什么了 这个字段里只有yes 空 和 no三个值可选 用这句语句查询出的结果的submit的值都是空值或者no ，sumbit值为yes 的记录显示不出来 ，这不是我的疑问 这是我说明这语句的查询出来的结果 我的疑问是


nvl(submit,'no')='no'的意思是什么了

[解决办法]
其实就相当于：

SQL code

String queryString = " from TProject where nvl(submit,'no') <> 'yes'
[解决办法]
SQL code
String queryString = " from TProject where nvl(submit,'no') = 'no' ";
[解决办法]
from TProject where nvl(submit,'no') = 'no'  

就是 
select * from TProject  where submit is null;
[解决办法]
探讨


from TProject where nvl(submit,'no') = 'no' 

就是  
select * from TProject  where submit is null;

[解决办法]
测试数据：
SQL code
CREATE TABLE TProject(    ID NUMBER(4),    sub VARCHAR2(20)    );INSERT INTO TProject VALUES(1, 'yes');INSERT INTO TProject VALUES(2, 'no');INSERT INTO TProject VALUES(3, NULL);