COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM Contacts WHERE FirstName = 'Test'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT Id) AS DistinctValues FROM Contacts WHERE FirstName = 'Test'

AVG

Returns the average of the column values.

SELECT CustomerName, AVG(AnnualRevenue) FROM Contacts WHERE FirstName = 'Test'  GROUP BY CustomerName

MIN

Returns the minimum column value.

SELECT MIN(AnnualRevenue), CustomerName FROM Contacts WHERE FirstName = 'Test' GROUP BY CustomerName

MAX

Returns the maximum column value.

SELECT CustomerName, MAX(AnnualRevenue) FROM Contacts WHERE FirstName = 'Test' GROUP BY CustomerName

SUM

Returns the total sum of the column values.

SELECT SUM(AnnualRevenue) FROM Contacts WHERE FirstName = 'Test'