This shows that the student whose number is 1011 took four course offerings
and repeated cs110. Note that for a partial rollup no general total is produced.
The rollup extension is especially useful when there exists a natural order
on the attributes of a table, as is in the next example.
Example 5.17.14 Suppose that we have the table SALES that contains records
of sales in a chain of department stores that is present in several regions of the
country: the North East (NE), South East (SE), and Midwest (MW).