This section describes aggregates (also described as set functions in ANSI SQL-92 and as column functions in some database literature). They provide a means of evaluating an expression over a set of rows. Whereas the other built-in functions operate on a single expression, aggregates operate on a set of values and reduce them to a single scalar value. Built-in aggregates can calculate the minimum, maximum, sum, count, and average of an expression over a set of values as well as count rows. You can also create your own aggregates to perform other set functions such as calculating the standard deviation.
-- not valid SELECT MIN(flying_time), flight_id FROM Flights
SELECT c1 FROM t1 GROUP BY c1 HAVING c2 > (SELECT t2.x FROM t2 WHERE t2.y = SUM(t1.c3))
A cursor declared on a ResultSet that includes an aggregate in the outer query block is not updatable.