COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM People WHERE Id = 'MyId'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT Id) AS DistinctValues FROM People WHERE Id = 'MyId'

AVG

Returns the average of the column values.

SELECT Firstname, AVG(AnnualRevenue) FROM People WHERE Id = 'MyId'  GROUP BY Firstname

MIN

Returns the minimum column value.

SELECT MIN(AnnualRevenue), Firstname FROM People WHERE Id = 'MyId' GROUP BY Firstname

MAX

Returns the maximum column value.

SELECT Firstname, MAX(AnnualRevenue) FROM People WHERE Id = 'MyId' GROUP BY Firstname

SUM

Returns the total sum of the column values.

SELECT SUM(AnnualRevenue) FROM People WHERE Id = 'MyId'