If you don't want the case setting to apply to your entire session, just use the case-changing functions in your select statement:
SELECT col1, col2, ...,coln
FROM my_table
WHERE UPPER(employee_name) = 'SMITH';
One thing I have seen people do that really screws up the works is to forget what their target string should look like:
SELECT col1, col2, ...,coln
FROM my_table
WHERE UPPER(employee_name) = 'Smith'; <=== This will guarantee "No Data Found"!