COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM incident WHERE category = 'request'

COUNT(DISTINCT)

Returns the number of distinct, non-null field values matching the query criteria.

SELECT COUNT(DISTINCT sys_id) AS DistinctValues FROM incident WHERE category = 'request'

AVG

Returns the average of the column values.

SELECT priority, AVG(priority) FROM incident WHERE category = 'request'  GROUP BY priority

MIN

Returns the minimum column value.

SELECT MIN(priority), priority FROM incident WHERE category = 'request' GROUP BY priority

MAX

Returns the maximum column value.

SELECT priority, MAX(priority) FROM incident WHERE category = 'request' GROUP BY priority

SUM

Returns the total sum of the column values.

SELECT SUM(priority) FROM incident WHERE category = 'request'