COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM Accounts WHERE ModifiedBy = 'System'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT AccountId) AS DistinctValues FROM Accounts WHERE ModifiedBy = 'System'

AVG

Returns the average of the column values.

SELECT AccountNumber, AVG(AnnualRevenue) FROM Accounts WHERE ModifiedBy = 'System'  GROUP BY AccountNumber

MIN

Returns the minimum column value.

SELECT MIN(AnnualRevenue), AccountNumber FROM Accounts WHERE ModifiedBy = 'System' GROUP BY AccountNumber

MAX

Returns the maximum column value.

SELECT AccountNumber, MAX(AnnualRevenue) FROM Accounts WHERE ModifiedBy = 'System' GROUP BY AccountNumber

SUM

Returns the total sum of the column values.

SELECT SUM(AnnualRevenue) FROM Accounts WHERE ModifiedBy = 'System'