There are many functions available on a database to do aggregated calculations. So they can be referred as aggregate functions. The aggregate functions available are:
count: To get the the number of rows with a specified criteria.
sum: To get the sum of values on the selected cells.
max: To get the maximum value within a selected range of data.
min: To get the minimum value within a selected range of data.
avg: To get the average of the selected data.
As the field name referred here is 'lastname', the appropriate aggregate function would be count.
The absolute value of 4/13 is 4/13 because when you put something in absolute value it becomes positive and sense this is already positive it stays. hope this helps :))))
