Question

Is this query valid? if the package(with proper definition and body) and function exists and works fine.

Select "JK" As Name, 
       pckg_name1.function_name1(number1,number2) 
from dual 

Answer 1

The function call is fine (assuming the function returns a SQL data type – you cannot use PL/SQL specific data types, e.g. Boolean), but your quoting for JK is wrong. You have to use single quotes instead of double ones:

Select 'JK' As Name, 
       pckg_name1.function_name1(number1,number2) 
from dual