Aggregate functions last() is not working as expected

Summary

last() should return last row of the data set, but it is fetching all the records.

Content

Objects : a) Incident b) CO.AuditLog (Custom Object).

Joining Relationship: 1: M (1 Incident : M AuditLog)

Requirement: New report to be developed to show only the last action performed on the incident.

CO.AuditLog has following attributes: ID, CreatedTime, FieldChanged, Value, Incident (Joining attribute)

I am trying to meet this requirement using Last() aggregate function, as per the documentation provided by oracle the syntax should be

last(expr, sort column1[, sort column2][,....]) 

For my requirement I have updated values as shown below:

Last(CO$AuditLog.ID, CO$AuditLog.CreatedTime)  - (Attached Report Defination)