An aggregate function is a function that performs a calculation on a set of values, and returns a single value.
Aggregate functions are often used with the GROUP BY clause of the SELECT statement. The GROUP BY clause splits the result-set into groups of values and the aggregate function can be used to return a single value for each group.
The most commonly used SQL aggregate functions are:
- MIN() - returns the smallest value of a column
- MAX() - returns the largest value of a column
- COUNT() - returns the number of rows in a set
- SUM() - returns the sum of a numerical column
- AVG() - returns the average value of a numerical column
Aggregate functions ignore null values (except for COUNT(*) ).
We will go through the aggregate functions above in the next chapters.