Use case
Return the sum of story points of the sibling issues including the current issue in the status category Done.
Expression
Create and configure a Smart field using this expression in General parsing mode:
%{sum(fieldValue({issue.cfnnnnn},issuesFromJQL("statusCategory = Done AND 'parent' = "+%{parent.key})))}
Replace "nnnnn" with the ID of the story points field. Keep in mind, that this smart fields should be displayed on a child issue.
