How to use MYSQL GROUP BY SUM with multiple columns

[Marco Antonio Marco]

Basically the question is how to get the sum from #hours, groupping by #id, #code, #semester, #year columns from this

id, hours, code, semester, year
165, 6, 3, 1, 2012
166, 6, 16, 1, 2012
460, 8, 14, 2, 2012
461, 8, 16, 2, 2012
462, 15, 16, 2, 2013
463, 6, 1, 2, 2013

id, hours, code, semester, year, sum
165, 6, 3, 1, 2012, ?
166, 6, 16, 1, 2012, ?
460, 8, 14, 2, 2012, ?
461, 8, 16, 2, 2012, ?
462, 15, 16, 2, 2013, ?
463, 6, 1, 2, 2013, ?

I have tried a lot with GROUP BY, GROUP BY CONCAT, etc, but no success.

I want to group by all these columns in each row