Aggregate Functions - max
Applies to: 
SQL Server
Returns from a sequence of atomic values, $arg, the one item whose value is greater than that of all the others.
Syntax
fn:max($arg as xdt:anyAtomicType*) as xdt:anyAtomicType?
Arguments
$arg
Sequence of atomic values from which to return the maximum value.
Remarks
All types of the atomized values that are passed to max() have to be subtypes of the same base type. Base types that are accepted are the types that support the gt operation. These types include the three built-in numeric base types, the date/time base types, xs:string, xs:boolean, and xdt:untypedAtomic. Values of type xdt:untypedAtomic are cast to xs:double. If there is a mixture of these types, or if other values of other types are passed, a static error is raised.
The result of max() receives the base type of the passed in types, such as xs:double in the case of xdt:untypedAtomic. If the input is statically empty, empty is implied and a static error is raised.
The max() function returns the one value in the sequence that is greater than any other in the input sequence. For xs:string values, the default Unicode Codepoint Collation is being used. If an xdt:untypedAtomic value cannot be cast to xs:double, the value is ignored in the input sequence, $arg. If the input is a dynamically calculated empty sequence, the empty sequence is returned.
Examples
This topic provides XQuery examples against XML instances that are stored in various xml type columns in the AdventureWorks2022 database.
A. Using the max() XQuery function to find work center locations in the manufacturing process that have the most labor hours
The query provided in min function (XQuery) can be rewritten to use the max() function.
Implementation Limitations
These are the limitations:
The max() function maps all integers to xs:decimal.
The max() function on values of type xs:duration is not supported.
Sequences that mix types across base type boundaries are not supported.
The syntactic option that provides a collation is not supported.