Null & Zero in SQL Server

A value of NULL indicates that the value is unknown.
 A value of NULL is different from an empty or zero value.
No two null values are equal. Comparisons between two null values, or between a NULL and any other value,
return unknown because the value of each NULL is unknown.

create table test_null 

( 

tid int identity(1,1),  

t_val varchar(20))  ;

go
 

insert into test_null(t_val) values(default)  

go 20 

select * from test_null where t_val = null

go 

--You will not get any output coz Ansi null is ON 

SET ANSI_NULLS  Off

select * from test_null 

where t_val = null

--Now you'll get all Null Values.