Suppose you want to retrieve the records
SELECT first_name, last_name, phone_number
FROM emp
WHERE UPPER(last_name) = UPPER('xYz123')
though index is on last_name it won't work as
the index is not on UPPER(last_name)
if you want to good execution plan
we need to create a index on as follows
CREATE INDEX emp_up_name
ON employees (UPPER(last_name))
this is called function-based index..
then only the performance will be increased
