To sort this table Employee by department, you would use ORDER BY Department. However, if you want a different sort order that is not alphabetical, you have to map the Department values into different values that sort correctly; this can be done with a CASE expression:

Name | Department | —–– | ––––– | Hasan | IT | Yusuf | HR | Hillary | HR | Joe | IT | Merry | HR | Ken | Accountant |

SELECT *
FROM Employee
ORDER BY CASE Department
         WHEN 'HR'         THEN 1
         WHEN 'Accountant' THEN 2
         ELSE                   3
         END;

Name | Department | —–– | ––––––– | Yusuf | HR | Hillary | HR | Merry | HR | Ken | Accountant | Hasan | IT | Joe | IT |