MAX (Transact-SQL)

ALL

Applies the aggregate function to all values. ALL is the default.

DISTINCT

Specifies that each unique value is considered. DISTINCT is not meaningful with MAX and is available for ISO compatibility only.

expression

Is a constant, column name, or function, and any combination of arithmetic, bitwise, and string operators. MAX can be used with numeric, character, and datetime columns, but not with bit columns. Aggregate functions and subqueries are not permitted.

For more information, see Expressions (Transact-SQL).

Returns a value same as expression.

MAX ignores any null values.

For character columns, MAX finds the highest value in the collating sequence.

The following example returns the highest (maximum) tax rate.

USE AdventureWorks2008R2;
GO
SELECT MAX(TaxRate)
FROM Sales.SalesTaxRate;
GO

Here is the result set.

------

19.60

(1 row(s) affected)

Warning, null value eliminated from aggregate.

Reference