COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM Contact WHERE Country = 'U.S.A.'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT SalesPerson) AS DistinctValues FROM Contact WHERE Country = 'U.S.A.'

AVG

Returns the average of the column values.

SELECT Name, AVG(AnnualRevenue) FROM Contact WHERE Country = 'U.S.A.'  GROUP BY Name

MIN

Returns the minimum column value.

SELECT MIN(AnnualRevenue), Name FROM Contact WHERE Country = 'U.S.A.' GROUP BY Name

MAX

Returns the maximum column value.

SELECT Name, MAX(AnnualRevenue) FROM Contact WHERE Country = 'U.S.A.' GROUP BY Name

SUM

Returns the total sum of the column values.

SELECT SUM(AnnualRevenue) FROM Contact WHERE Country = 'U.S.A.'