COUNT

Returns the number of rows matching the query criteria.

SELECT COUNT(*) FROM Files WHERE Id = '123'

COUNT(DISTINCT)

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

SELECT COUNT(DISTINCT Id) AS DistinctValues FROM Files WHERE Id = '123'

AVG

Returns the average of the column values.

SELECT Name, AVG(Size) FROM Files WHERE Id = '123'  GROUP BY Name

MIN

Returns the minimum column value.

SELECT MIN(Size), Name FROM Files WHERE Id = '123' GROUP BY Name

MAX

Returns the maximum column value.

SELECT Name, MAX(Size) FROM Files WHERE Id = '123' GROUP BY Name

SUM

Returns the total sum of the column values.

SELECT SUM(Size) FROM Files WHERE Id = '123'