Returns the maximum expression value found in each group of rows.
MAX ( expression | DISTINCT column-name )
expression The expression for which the maximum value is to be calculated. This is commonly a column name.
DISTINCT column-name Returns the same as MAX ( expression ), and is included for completeness.
The following statement returns the value 138948.000, representing the maximum salary in the Employees table:
SELECT MAX ( Salary ) FROM Employees
Rows where expression is NULL are ignored. Returns NULL for a group containing no rows.
Chapter 2, “Using OLAP” in the System Administration Guide: Volume 2