MAX is an aggregate function that evaluates the maximum of an
expression over a set of rows (see
The
DISTINCT and ALL qualifiers eliminate or retain duplicates, but
these qualifiers have no effect in a MAX expression. Only one DISTINCT aggregate
expression per
The Expression can contain multiple column references or expressions, but it cannot contain another aggregate or subquery. It must evaluate to a built-in data type. You can therefore call methods that evaluate to built-in data types. (For example, a method that returns a java.lang.Integer or int evaluates to an INTEGER.) If an expression evaluates to NULL, the aggregate skips that value.
The type's comparison rules determine the maximum value. For CHAR and VARCHAR, the number of blank spaces at the end of the value can affect how MAX is evaluated. For example, if the values 'z' and 'z ' are both stored in a column, you cannot control which one will be returned as the maximum, because blank spaces are ignored for character comparisons.
The resulting data type is the same as the expression on which it operates (it will never overflow).