• How do I get Year or Month etc From Date?
  Use the Extract Function

SELECT EXTRACT(MONTH FROM ORDER_DATE) ORDER_MONTH FROM ORDERS;

• Can I use aliases in where clause?
  The answer is No

SELECT EXTRACT(MONTH FROM ORDER_DATE) ORDER_MONTH FROM ORDERS WHERE ORDER_MONTH = 10;--don't do this

SELECT EXTRACT(MONTH FROM ORDER_DATE) ORDER_MONTH FROM ORDERS WHERE EXTRACT(MONTH FROM ORDER_DATE) = 10;--do like this