There is nothing exactly  like negative test case.
If we test with negative data, then it is called negative 
testing. So no need to add new column for this.
For ex : There is a text box. According to the validation 
it will take only alphanumeric value according to the SRS 
(like 12gh, amit, amit 1234, 11amit). In this case enter 
some special characters in that field ($&)@!) to know 
whether it is accepting that or not. It is called negative 
testing.