Hi Sumet,
Sum works only on a numeric value MARKS seems to be alpha numeric. Distinct is not necessary because this is done through the aggregation node already.
Aggregation and Projection can have the same result but doesn't have to. Aggregation is in my understanding comparable to a group by in SQL. In a projection node you are for example not able to create aggregated values.
What do you mean with the raw table question? Do you mean row table?
Best regards
Patrik