Article Views - Authors Who Viewed Their Own Articles
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Article Views - Authors Who Viewed Their Own Articles
You are given a Views table that logs which viewer read which article on a given date. There is no primary key, so duplicate rows can exist. Write a SQL query to find all authors who have viewed at least one of their own articles - i.e., rows where author_id = viewer_id. Return the result as id, sorted in ascending order.
Examples
Author 7 viewed their own article (article_id=2). Author 4 viewed their own article (article_id=3) - the duplicate row is ignored by DISTINCT. Author 3 never viewed their own articles.
Approach hint
Start with a simple approach, explain the trade-off, then move toward a cleaner or more scalable solution.
Common mistake
Skipping assumptions, edge cases, or trade-offs can make an otherwise good answer feel incomplete.