Compute reservation diff for largest member
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This question evaluates competency in relational data manipulation and aggregation using SQL or Python, including joins, grouping, and handling missing referrer relationships.
Given copies(copy_id, reserved_by_member_id) and members(member_id, referred_by_member_id), find the member with the largest member_id. Return a single row with: member_id, referred_by_member_id, and diff_of_reserved_copy_num defined as (number of copies reserved by that member) minus (number of copies reserved by their referrer). If the referrer is NULL or has no reservations, treat their count as 0.
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