How would you handle NULL problems?

Question

(ie. NULL - 25 = ?)​

Answer 1

 create table tbltest
(
id int identity(1,1),
name varchar(12),
city varchar(200)
)
insert into tbltest(name,city)values
('a',NULL)
,('b','Meerut')
,('c','Rampur')
,('d',NULL)
,('e',NULL)
,('f','NOIDA')

select *from tbltest

 select *from tbltest where isnull(city,'')<>'merrut'