- You can apply
more than one (set) function
on the groups
- Each set function
will produce
one value for each group
- So, you will get a "vector" (or array) of function values
- Example:
-
Find the
average salary
and
number of employees
for males and females
for each department
We must first form groups of employee tuples based on their DNO and sex attributes (grouped by department number and sex)
And then compute average Salary and count the SSN of employees:
- The Result relation is:
DNO sex Avg Count +--------+-----------+------------+------+ | 4 | M | 45000 | 2 | +--------+-----------+------------+------+ | 5 | M | 60000 | 1 | +--------+-----------+------------+------+ | 5 | F | 50000 | 1 | +--------+-----------+------------+------+