Using GROUP BY with the WITH ROLLUP Modifier

MySQL provides a variety of aggregate functions. Without a GROUP BY clause in a SELECT statement, aggregating expressions apply to all row values of the referred table, yielding a single result row. This behavior is desirable if we want to compute the AVG() over a set of values, for example. On the contrary, this behavior is not helpful if the underlying table’s dataset clusters into different groups. Recalling the table of our running example, CarModel, its data points naturally fall into groups: