When the “ROLLUP” operator for expression or columns within a “GROUP BY” clause is used?

[answerhappygod]

a) Find the groups that make up the subtotal in a row
b) Create group-wise grand totals for the groups indicated in a GROUP BY clause
c) Group expressions or columns specified in a GROUP BY clause in one direction, from right to left, for computing the subtotals
d) To produce a cross-tabular report for computing subtotals by grouping phrases or columns given within a GROUP BY clause in all available directions