What will happen,when we execute below query?

Select Substring('Vishal Kumar','Neeraj',10) as Portion;

Answer:

It will give us below error:

Msg 8116, Level 16, State 1, Line 1
Argument data type varchar is invalid for argument 2 of substring function.

Meaning that,we can not pass varchar value in 2nd and 3rd parameter because substring function takes integer value in 2nd and 3rd parameter that is start_position and string_length.
so always give numeric value in start_position and string_length parameter.