GROUP BY is a way to sub-total your results, or perform some other "aggregate" function on them.
Example :
SELECT department, sum(salary)
FROM tblEmployee
GROUP BY department;
will give you salary totals by department, whereas the sum statement by itself would just give you the grand total of all salaries in tblEmployee.
ORDER BY is simply a way to sort your results - it does not affect what shows up in your resultset, only what order it is displayed.
Example :
SELECT *
FROM tblEmployee
ORDER BY lastname;
will give you all tblEmployee data, in order of last name. If you want the results in descending (reversed) order, simply add DESC to the end of the clause :
ORDER BY lastname DESC;
