COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM Orders WHERE ParentId = '3'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT ParentId) AS DistinctValues FROM Orders WHERE ParentId = '3'

AVG

Returns the average of the column values.

SELECT Total, AVG(AnnualRevenue) FROM Orders WHERE ParentId = '3'  GROUP BY Total

MIN

Returns the minimum column value.

SELECT MIN(AnnualRevenue), Total FROM Orders WHERE ParentId = '3' GROUP BY Total

MAX

Returns the maximum column value.

SELECT Total, MAX(AnnualRevenue) FROM Orders WHERE ParentId = '3' GROUP BY Total

SUM

Returns the total sum of the column values.

SELECT SUM(AnnualRevenue) FROM Orders WHERE ParentId = '3'